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 $204.73   8.613%   $222.3634   $222.36   $222.35   $222.40  
  Purchase #2 $68.32   10.679%   $75.6159   $75.62   $75.60   $75.60  
  Purchase #3 $142.78   10.454%   $157.7062   $157.71   $157.70   $157.70  
  Purchase #4 $54.49   9.401%   $59.6126   $59.61   $59.60   $59.60  
  Purchase #5 $84.74   12.759%   $95.552   $95.55   $95.55   $95.60  
  Purchase #6 $207.32   9.590%   $227.202   $227.20   $227.20   $227.20  
  Purchase #7 $88.91   7.342%   $95.4378   $95.44   $95.45   $95.40  
  7 purchase totals = $851.29       $933.4899   $933.49   $933.45   $933.50