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 $64.67   7.638%   $69.6095   $69.61   $69.60   $69.60  
  Purchase #2 $27.97   12.142%   $31.3661   $31.37   $31.35   $31.40  
  Purchase #3 $56.75   10.632%   $62.7837   $62.78   $62.80   $62.80  
  Purchase #4 $94.97   10.817%   $105.2429   $105.24   $105.25   $105.20  
  Purchase #5 $237.98   12.312%   $267.2801   $267.28   $267.30   $267.30  
  Purchase #6 $186.36   4.620%   $194.9698   $194.97   $194.95   $195.00  
  Purchase #7 $217.38   3.692%   $225.4057   $225.41   $225.40   $225.40  
  7 purchase totals = $886.08       $956.6578   $956.66   $956.65   $956.70