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 $178.63   12.791%   $201.4786   $201.48   $201.50   $201.50  
  Purchase #2 $183.77   5.485%   $193.8498   $193.85   $193.85   $193.80  
  Purchase #3 $85.40   10.407%   $94.2876   $94.29   $94.30   $94.30  
  Purchase #4 $44.74   4.352%   $46.6871   $46.69   $46.70   $46.70  
  Purchase #5 $217.68   5.647%   $229.9724   $229.97   $229.95   $230.00  
  Purchase #6 $30.79   12.547%   $34.6532   $34.65   $34.65   $34.70  
  Purchase #7 $21.81   11.531%   $24.3249   $24.32   $24.30   $24.30  
  7 purchase totals = $762.82       $825.2536   $825.25   $825.25   $825.30