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 $237.38   7.674%   $255.5965   $255.60   $255.60   $255.60  
  Purchase #2 $217.89   8.157%   $235.6633   $235.66   $235.65   $235.70  
  Purchase #3 $161.52   8.643%   $175.4802   $175.48   $175.50   $175.50  
  Purchase #4 $236.86   3.162%   $244.3495   $244.35   $244.35   $244.30  
  Purchase #5 $199.31   3.342%   $205.9709   $205.97   $205.95   $206.00  
  Purchase #6 $140.45   10.318%   $154.9416   $154.94   $154.95   $154.90  
  Purchase #7 $92.76   3.483%   $95.9908   $95.99   $96.00   $96.00  
  7 purchase totals = $1,286.17       $1,367.9928   $1,367.99   $1,368.00   $1,368.00