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 $51.75   11.747%   $57.8291   $57.83   $57.85   $57.80  
  Purchase #2 $239.96   7.533%   $258.0362   $258.04   $258.05   $258.00  
  Purchase #3 $123.36   6.537%   $131.424   $131.42   $131.40   $131.40  
  Purchase #4 $225.52   3.838%   $234.1755   $234.18   $234.20   $234.20  
  Purchase #5 $158.40   10.810%   $175.523   $175.52   $175.50   $175.50  
  Purchase #6 $118.50   6.316%   $125.9845   $125.98   $126.00   $126.00  
  Purchase #7 $60.46   4.494%   $63.1771   $63.18   $63.20   $63.20  
  7 purchase totals = $977.95       $1,046.1494   $1,046.15   $1,046.20   $1,046.10