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 $114.88   10.593%   $127.0492   $127.05   $127.05   $127.00  
  Purchase #2 $182.52   6.819%   $194.966   $194.97   $194.95   $195.00  
  Purchase #3 $133.55   6.770%   $142.5913   $142.59   $142.60   $142.60  
  Purchase #4 $112.38   11.315%   $125.0958   $125.10   $125.10   $125.10  
  Purchase #5 $38.41   7.352%   $41.2339   $41.23   $41.25   $41.20  
  Purchase #6 $105.56   6.310%   $112.2208   $112.22   $112.20   $112.20  
  Purchase #7 $210.89   3.245%   $217.7334   $217.73   $217.75   $217.70  
  7 purchase totals = $898.19       $960.8904   $960.89   $960.90   $960.80