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 $188.82   13.226%   $213.7933   $213.79   $213.80   $213.80  
  Purchase #2 $112.87   4.506%   $117.9559   $117.96   $117.95   $118.00  
  Purchase #3 $193.28   6.697%   $206.224   $206.22   $206.20   $206.20  
  Purchase #4 $205.90   8.481%   $223.3624   $223.36   $223.35   $223.40  
  Purchase #5 $51.32   5.791%   $54.2919   $54.29   $54.30   $54.30  
  Purchase #6 $29.29   11.266%   $32.5898   $32.59   $32.60   $32.60  
  Purchase #7 $108.94   13.602%   $123.758   $123.76   $123.75   $123.80  
  7 purchase totals = $890.42       $971.9753   $971.97   $971.95   $972.10