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 $224.44   12.127%   $251.6578   $251.66   $251.65   $251.70  
  Purchase #2 $56.38   6.621%   $60.1129   $60.11   $60.10   $60.10  
  Purchase #3 $177.93   11.158%   $197.7834   $197.78   $197.80   $197.80  
  Purchase #4 $170.95   11.456%   $190.534   $190.53   $190.55   $190.50  
  Purchase #5 $16.64   8.293%   $18.02   $18.02   $18.00   $18.00  
  Purchase #6 $117.91   11.143%   $131.0487   $131.05   $131.05   $131.00  
  Purchase #7 $155.36   7.599%   $167.1658   $167.17   $167.15   $167.20  
  7 purchase totals = $919.61       $1,016.3226   $1,016.32   $1,016.30   $1,016.30