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 $88.55   6.333%   $94.1579   $94.16   $94.15   $94.20  
  Purchase #2 $200.71   4.586%   $209.9146   $209.91   $209.90   $209.90  
  Purchase #3 $61.70   7.647%   $66.4182   $66.42   $66.40   $66.40  
  Purchase #4 $182.74   13.771%   $207.9051   $207.91   $207.90   $207.90  
  Purchase #5 $227.90   4.763%   $238.7549   $238.75   $238.75   $238.80  
  Purchase #6 $5.51   12.773%   $6.2138   $6.21   $6.20   $6.20  
  Purchase #7 $170.30   11.654%   $190.1468   $190.15   $190.15   $190.10  
  7 purchase totals = $937.41       $1,013.5113   $1,013.51   $1,013.45   $1,013.50