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 $61.95   9.579%   $67.8842   $67.88   $67.90   $67.90  
  Purchase #2 $127.60   6.641%   $136.0739   $136.07   $136.05   $136.10  
  Purchase #3 $43.56   6.453%   $46.3709   $46.37   $46.35   $46.40  
  Purchase #4 $206.29   6.534%   $219.769   $219.77   $219.75   $219.80  
  Purchase #5 $135.57   8.123%   $146.5824   $146.58   $146.60   $146.60  
  Purchase #6 $71.63   6.717%   $76.4414   $76.44   $76.45   $76.40  
  Purchase #7 $229.38   5.748%   $242.5648   $242.56   $242.55   $242.60  
  7 purchase totals = $875.98       $935.6866   $935.67   $935.65   $935.80