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 $60.73   9.244%   $66.3439   $66.34   $66.35   $66.30  
  Purchase #2 $117.65   7.353%   $126.3008   $126.30   $126.30   $126.30  
  Purchase #3 $71.90   4.379%   $75.0485   $75.05   $75.05   $75.00  
  Purchase #4 $65.29   6.584%   $69.5887   $69.59   $69.60   $69.60  
  Purchase #5 $175.39   5.738%   $185.4539   $185.45   $185.45   $185.50  
  Purchase #6 $26.92   12.872%   $30.3851   $30.39   $30.40   $30.40  
  Purchase #7 $49.62   4.261%   $51.7343   $51.73   $51.75   $51.70  
  7 purchase totals = $567.50       $604.8552   $604.85   $604.90   $604.80