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 $182.51   10.243%   $201.2045   $201.20   $201.20   $201.20  
  Purchase #2 $189.46   5.311%   $199.5222   $199.52   $199.50   $199.50  
  Purchase #3 $70.92   3.529%   $73.4228   $73.42   $73.40   $73.40  
  Purchase #4 $26.79   9.641%   $29.3728   $29.37   $29.35   $29.40  
  Purchase #5 $229.73   9.222%   $250.9157   $250.92   $250.90   $250.90  
  Purchase #6 $148.37   8.839%   $161.4844   $161.48   $161.50   $161.50  
  Purchase #7 $61.42   6.697%   $65.5333   $65.53   $65.55   $65.50  
  7 purchase totals = $909.20       $981.4557   $981.44   $981.40   $981.40