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 $50.44   9.853%   $55.4099   $55.41   $55.40   $55.40  
  Purchase #2 $43.80   9.812%   $48.0977   $48.10   $48.10   $48.10  
  Purchase #3 $181.28   4.110%   $188.7306   $188.73   $188.75   $188.70  
  Purchase #4 $191.76   12.619%   $215.9582   $215.96   $215.95   $216.00  
  Purchase #5 $48.68   11.190%   $54.1273   $54.13   $54.15   $54.10  
  Purchase #6 $102.52   7.853%   $110.5709   $110.57   $110.55   $110.60  
  Purchase #7 $232.68   6.771%   $248.4348   $248.43   $248.45   $248.40  
  7 purchase totals = $851.16       $921.3294   $921.33   $921.35   $921.30