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 $182.75   10.656%   $202.2238   $202.22   $202.20   $202.20  
  Purchase #2 $96.64   6.178%   $102.6104   $102.61   $102.60   $102.60  
  Purchase #3 $225.96   8.343%   $244.8118   $244.81   $244.80   $244.80  
  Purchase #4 $19.46   5.136%   $20.4595   $20.46   $20.45   $20.50  
  Purchase #5 $20.63   13.326%   $23.3792   $23.38   $23.40   $23.40  
  Purchase #6 $160.25   3.762%   $166.2786   $166.28   $166.30   $166.30  
  Purchase #7 $223.43   5.537%   $235.8013   $235.80   $235.80   $235.80  
  7 purchase totals = $929.12       $995.5646   $995.56   $995.55   $995.60