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 $188.71   8.459%   $204.673   $204.67   $204.65   $204.70  
  Purchase #2 $217.50   12.623%   $244.955   $244.96   $244.95   $245.00  
  Purchase #3 $107.64   8.471%   $116.7582   $116.76   $116.75   $116.80  
  Purchase #4 $51.85   12.480%   $58.3209   $58.32   $58.30   $58.30  
  Purchase #5 $24.68   5.585%   $26.0584   $26.06   $26.05   $26.10  
  Purchase #6 $149.37   7.438%   $160.4801   $160.48   $160.50   $160.50  
  Purchase #7 $163.73   7.642%   $176.2422   $176.24   $176.25   $176.20  
  7 purchase totals = $903.48       $987.4878   $987.49   $987.45   $987.60