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 $205.82   10.758%   $227.9621   $227.96   $227.95   $228.00  
  Purchase #2 $227.43   9.634%   $249.3406   $249.34   $249.35   $249.30  
  Purchase #3 $98.99   10.348%   $109.2335   $109.23   $109.25   $109.20  
  Purchase #4 $146.37   12.530%   $164.7102   $164.71   $164.70   $164.70  
  Purchase #5 $236.60   4.213%   $246.568   $246.57   $246.55   $246.60  
  Purchase #6 $221.65   9.108%   $241.8379   $241.84   $241.85   $241.80  
  Purchase #7 $90.32   4.106%   $94.0285   $94.03   $94.05   $94.00  
  7 purchase totals = $1,227.18       $1,333.6808   $1,333.68   $1,333.70   $1,333.60