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 $210.55   3.520%   $217.9614   $217.96   $217.95   $218.00  
  Purchase #2 $119.25   11.686%   $133.1856   $133.19   $133.20   $133.20  
  Purchase #3 $118.36   5.534%   $124.91   $124.91   $124.90   $124.90  
  Purchase #4 $221.36   13.163%   $250.4976   $250.50   $250.50   $250.50  
  Purchase #5 $99.59   5.122%   $104.691   $104.69   $104.70   $104.70  
  Purchase #6 $67.94   9.507%   $74.3991   $74.40   $74.40   $74.40  
  Purchase #7 $84.39   13.493%   $95.7767   $95.78   $95.80   $95.80  
  7 purchase totals = $921.44       $1,001.4214   $1,001.43   $1,001.45   $1,001.50