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 $52.53   3.238%   $54.2309   $54.23   $54.25   $54.20  
  Purchase #2 $54.73   13.744%   $62.2521   $62.25   $62.25   $62.30  
  Purchase #3 $107.68   10.480%   $118.9649   $118.96   $118.95   $119.00  
  Purchase #4 $218.85   3.549%   $226.617   $226.62   $226.60   $226.60  
  Purchase #5 $96.50   11.216%   $107.3234   $107.32   $107.30   $107.30  
  Purchase #6 $174.25   13.503%   $197.779   $197.78   $197.80   $197.80  
  Purchase #7 $103.37   10.201%   $113.9148   $113.91   $113.90   $113.90  
  7 purchase totals = $807.91       $881.0821   $881.07   $881.05   $881.10