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 $131.77   12.521%   $148.2689   $148.27   $148.25   $148.30  
  Purchase #2 $54.82   11.868%   $61.326   $61.33   $61.35   $61.30  
  Purchase #3 $199.85   3.834%   $207.5122   $207.51   $207.50   $207.50  
  Purchase #4 $71.40   5.512%   $75.3356   $75.34   $75.35   $75.30  
  Purchase #5 $236.59   7.361%   $254.0054   $254.01   $254.00   $254.00  
  Purchase #6 $158.83   11.581%   $177.2241   $177.22   $177.20   $177.20  
  Purchase #7 $27.75   3.161%   $28.6272   $28.63   $28.65   $28.60  
  7 purchase totals = $881.01       $952.2994   $952.31   $952.30   $952.20