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 $200.81   11.711%   $224.3269   $224.33   $224.35   $224.30  
  Purchase #2 $141.98   12.166%   $159.2533   $159.25   $159.25   $159.30  
  Purchase #3 $169.38   13.701%   $192.5868   $192.59   $192.60   $192.60  
  Purchase #4 $70.53   3.795%   $73.2066   $73.21   $73.20   $73.20  
  Purchase #5 $228.95   8.229%   $247.7903   $247.79   $247.80   $247.80  
  Purchase #6 $12.29   13.706%   $13.9745   $13.97   $13.95   $14.00  
  Purchase #7 $191.31   12.693%   $215.593   $215.59   $215.60   $215.60  
  7 purchase totals = $1,015.25       $1,126.7314   $1,126.73   $1,126.75   $1,126.80