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 $62.36   4.714%   $65.2997   $65.30   $65.30   $65.30  
  Purchase #2 $42.73   10.111%   $47.0504   $47.05   $47.05   $47.10  
  Purchase #3 $153.25   9.258%   $167.4379   $167.44   $167.45   $167.40  
  Purchase #4 $249.67   4.275%   $260.3434   $260.34   $260.35   $260.30  
  Purchase #5 $149.65   6.291%   $159.0645   $159.06   $159.05   $159.10  
  Purchase #6 $218.59   10.334%   $241.1791   $241.18   $241.20   $241.20  
  Purchase #7 $30.25   8.475%   $32.8137   $32.81   $32.80   $32.80  
  7 purchase totals = $906.50       $973.1887   $973.18   $973.20   $973.20