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 $58.92   7.490%   $63.3331   $63.33   $63.35   $63.30  
  Purchase #2 $233.96   6.765%   $249.7874   $249.79   $249.80   $249.80  
  Purchase #3 $104.61   13.826%   $119.0734   $119.07   $119.05   $119.10  
  Purchase #4 $169.38   4.659%   $177.2714   $177.27   $177.25   $177.30  
  Purchase #5 $166.62   13.117%   $188.4755   $188.48   $188.50   $188.50  
  Purchase #6 $75.68   5.133%   $79.5647   $79.56   $79.55   $79.60  
  Purchase #7 $144.36   12.560%   $162.4916   $162.49   $162.50   $162.50  
  7 purchase totals = $953.53       $1,039.9971   $1,039.99   $1,040.00   $1,040.10