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 $50.29   6.210%   $53.413   $53.41   $53.40   $53.40  
  Purchase #2 $127.54   8.512%   $138.3962   $138.40   $138.40   $138.40  
  Purchase #3 $199.95   6.673%   $213.2927   $213.29   $213.30   $213.30  
  Purchase #4 $226.46   8.216%   $245.066   $245.07   $245.05   $245.10  
  Purchase #5 $24.43   4.477%   $25.5237   $25.52   $25.50   $25.50  
  Purchase #6 $100.48   4.291%   $104.7916   $104.79   $104.80   $104.80  
  Purchase #7 $165.89   8.181%   $179.4615   $179.46   $179.45   $179.50  
  7 purchase totals = $895.04       $959.9447   $959.94   $959.90   $960.00