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 $192.62   7.636%   $207.3285   $207.33   $207.35   $207.30  
  Purchase #2 $69.59   6.217%   $73.9164   $73.92   $73.90   $73.90  
  Purchase #3 $59.34   9.413%   $64.9257   $64.93   $64.95   $64.90  
  Purchase #4 $148.43   13.639%   $168.6744   $168.67   $168.65   $168.70  
  Purchase #5 $57.53   7.665%   $61.9397   $61.94   $61.95   $61.90  
  Purchase #6 $169.59   7.748%   $182.7298   $182.73   $182.75   $182.70  
  Purchase #7 $139.90   8.377%   $151.6194   $151.62   $151.60   $151.60  
  7 purchase totals = $837.00       $911.1339   $911.14   $911.15   $911.00