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 $135.68   10.526%   $149.9617   $149.96   $149.95   $150.00  
  Purchase #2 $57.41   12.604%   $64.646   $64.65   $64.65   $64.60  
  Purchase #3 $237.35   11.633%   $264.9609   $264.96   $264.95   $265.00  
  Purchase #4 $155.88   7.552%   $167.6521   $167.65   $167.65   $167.70  
  Purchase #5 $207.82   13.729%   $236.3516   $236.35   $236.35   $236.40  
  Purchase #6 $225.76   11.290%   $251.2483   $251.25   $251.25   $251.20  
  Purchase #7 $243.90   13.453%   $276.7119   $276.71   $276.70   $276.70  
  7 purchase totals = $1,263.80       $1,411.5325   $1,411.53   $1,411.50   $1,411.60