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 $67.29   12.263%   $75.5418   $75.54   $75.55   $75.50  
  Purchase #2 $214.73   13.620%   $243.9762   $243.98   $244.00   $244.00  
  Purchase #3 $80.63   12.587%   $90.7789   $90.78   $90.80   $90.80  
  Purchase #4 $185.50   6.283%   $197.155   $197.16   $197.15   $197.20  
  Purchase #5 $49.83   4.168%   $51.9069   $51.91   $51.90   $51.90  
  Purchase #6 $173.25   5.304%   $182.4392   $182.44   $182.45   $182.40  
  Purchase #7 $108.77   5.798%   $115.0765   $115.08   $115.10   $115.10  
  7 purchase totals = $880.00       $956.8745   $956.89   $956.95   $956.90