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 $58.35   3.756%   $60.5416   $60.54   $60.55   $60.50  
  Purchase #2 $119.76   4.345%   $124.9636   $124.96   $124.95   $125.00  
  Purchase #3 $160.65   13.778%   $182.7844   $182.78   $182.80   $182.80  
  Purchase #4 $236.73   8.483%   $256.8118   $256.81   $256.80   $256.80  
  Purchase #5 $187.82   12.432%   $211.1698   $211.17   $211.15   $211.20  
  Purchase #6 $212.52   10.616%   $235.0811   $235.08   $235.10   $235.10  
  Purchase #7 $143.72   7.795%   $154.923   $154.92   $154.90   $154.90  
  7 purchase totals = $1,119.55       $1,226.2753   $1,226.26   $1,226.25   $1,226.30