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 $49.27   10.327%   $54.3581   $54.36   $54.35   $54.40  
  Purchase #2 $35.35   9.468%   $38.6969   $38.70   $38.70   $38.70  
  Purchase #3 $217.88   13.819%   $247.9888   $247.99   $248.00   $248.00  
  Purchase #4 $195.86   13.755%   $222.8005   $222.80   $222.80   $222.80  
  Purchase #5 $51.41   6.246%   $54.6211   $54.62   $54.60   $54.60  
  Purchase #6 $69.68   11.427%   $77.6423   $77.64   $77.65   $77.60  
  Purchase #7 $189.71   4.317%   $197.8998   $197.90   $197.90   $197.90  
  7 purchase totals = $809.16       $894.0075   $894.01   $894.00   $894.00