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 $223.46   12.613%   $251.645   $251.65   $251.65   $251.60  
  Purchase #2 $45.52   4.356%   $47.5029   $47.50   $47.50   $47.50  
  Purchase #3 $111.99   6.588%   $119.3679   $119.37   $119.35   $119.40  
  Purchase #4 $161.85   12.485%   $182.057   $182.06   $182.05   $182.10  
  Purchase #5 $208.52   6.542%   $222.1614   $222.16   $222.15   $222.20  
  Purchase #6 $10.71   8.603%   $11.6314   $11.63   $11.65   $11.60  
  Purchase #7 $61.74   9.214%   $67.4287   $67.43   $67.45   $67.40  
  7 purchase totals = $823.79       $901.7943   $901.80   $901.80   $901.80