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 $82.37   13.185%   $93.2305   $93.23   $93.25   $93.20  
  Purchase #2 $52.42   12.136%   $58.7817   $58.78   $58.80   $58.80  
  Purchase #3 $49.68   10.788%   $55.0395   $55.04   $55.05   $55.00  
  Purchase #4 $65.38   4.427%   $68.2744   $68.27   $68.25   $68.30  
  Purchase #5 $103.52   13.324%   $117.313   $117.31   $117.30   $117.30  
  Purchase #6 $72.36   4.315%   $75.4823   $75.48   $75.50   $75.50  
  Purchase #7 $59.90   11.136%   $66.5705   $66.57   $66.55   $66.60  
  7 purchase totals = $485.63       $534.6919   $534.68   $534.70   $534.70