Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.56   11.730%   $263.1912   $263.19   $263.20   $263.20  
  Purchase #2 $118.98   10.249%   $131.1743   $131.17   $131.15   $131.20  
  Purchase #3 $185.76   9.725%   $203.8252   $203.83   $203.85   $203.80  
  Purchase #4 $245.75   10.828%   $272.3598   $272.36   $272.35   $272.40  
  Purchase #5 $96.85   12.221%   $108.686   $108.69   $108.70   $108.70  
  Purchase #6 $209.71   12.593%   $236.1188   $236.12   $236.10   $236.10  
  Purchase #7 $156.48   13.475%   $177.5657   $177.57   $177.55   $177.60  
  7 purchase totals = $1,249.09       $1,392.9210   $1,392.93   $1,392.90   $1,393.00