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 $72.98   4.794%   $76.4787   $76.48   $76.50   $76.50  
  Purchase #2 $182.60   4.869%   $191.4908   $191.49   $191.50   $191.50  
  Purchase #3 $15.85   11.369%   $17.652   $17.65   $17.65   $17.70  
  Purchase #4 $150.68   12.328%   $169.2558   $169.26   $169.25   $169.30  
  Purchase #5 $78.84   7.362%   $84.6442   $84.64   $84.65   $84.60  
  Purchase #6 $186.86   4.272%   $194.8427   $194.84   $194.85   $194.80  
  Purchase #7 $29.52   9.474%   $32.3167   $32.32   $32.30   $32.30  
  7 purchase totals = $717.33       $766.6809   $766.68   $766.70   $766.70