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 $212.52   13.526%   $241.2655   $241.27   $241.25   $241.30  
  Purchase #2 $193.28   12.427%   $217.2989   $217.30   $217.30   $217.30  
  Purchase #3 $28.79   11.441%   $32.0839   $32.08   $32.10   $32.10  
  Purchase #4 $178.29   10.536%   $197.0746   $197.07   $197.05   $197.10  
  Purchase #5 $198.78   13.804%   $226.2196   $226.22   $226.20   $226.20  
  Purchase #6 $177.98   3.163%   $183.6095   $183.61   $183.60   $183.60  
  Purchase #7 $108.63   9.776%   $119.2497   $119.25   $119.25   $119.20  
  7 purchase totals = $1,098.27       $1,216.8017   $1,216.80   $1,216.75   $1,216.80