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 $177.61   7.593%   $191.0959   $191.10   $191.10   $191.10  
  Purchase #2 $65.59   9.673%   $71.9345   $71.93   $71.95   $71.90  
  Purchase #3 $157.88   5.655%   $166.8081   $166.81   $166.80   $166.80  
  Purchase #4 $101.59   10.469%   $112.2255   $112.23   $112.25   $112.20  
  Purchase #5 $202.51   3.668%   $209.9381   $209.94   $209.95   $209.90  
  Purchase #6 $89.85   13.517%   $101.995   $102.00   $102.00   $102.00  
  Purchase #7 $96.39   12.813%   $108.7405   $108.74   $108.75   $108.70  
  7 purchase totals = $891.42       $962.7376   $962.75   $962.80   $962.60