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 $26.71   11.170%   $29.6935   $29.69   $29.70   $29.70  
  Purchase #2 $53.95   11.530%   $60.1704   $60.17   $60.15   $60.20  
  Purchase #3 $102.32   12.775%   $115.3914   $115.39   $115.40   $115.40  
  Purchase #4 $182.50   12.322%   $204.9877   $204.99   $205.00   $205.00  
  Purchase #5 $58.86   6.224%   $62.5234   $62.52   $62.50   $62.50  
  Purchase #6 $154.80   9.646%   $169.732   $169.73   $169.75   $169.70  
  Purchase #7 $57.76   6.854%   $61.7189   $61.72   $61.70   $61.70  
  7 purchase totals = $636.90       $704.2173   $704.21   $704.20   $704.20