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 $204.27   3.272%   $210.9537   $210.95   $210.95   $211.00  
  Purchase #2 $86.75   12.444%   $97.5452   $97.55   $97.55   $97.50  
  Purchase #3 $169.26   13.115%   $191.4584   $191.46   $191.45   $191.50  
  Purchase #4 $15.55   6.260%   $16.5234   $16.52   $16.50   $16.50  
  Purchase #5 $27.36   6.151%   $29.0429   $29.04   $29.05   $29.00  
  Purchase #6 $133.57   12.215%   $149.8856   $149.89   $149.90   $149.90  
  Purchase #7 $124.64   9.314%   $136.249   $136.25   $136.25   $136.20  
  7 purchase totals = $761.40       $831.6582   $831.66   $831.65   $831.60