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 $135.38   8.288%   $146.6003   $146.60   $146.60   $146.60  
  Purchase #2 $86.72   7.411%   $93.1468   $93.15   $93.15   $93.10  
  Purchase #3 $79.50   13.492%   $90.2261   $90.23   $90.25   $90.20  
  Purchase #4 $185.46   12.339%   $208.3439   $208.34   $208.35   $208.30  
  Purchase #5 $202.34   8.602%   $219.7453   $219.75   $219.75   $219.70  
  Purchase #6 $125.96   10.582%   $139.2891   $139.29   $139.30   $139.30  
  Purchase #7 $99.79   13.210%   $112.9723   $112.97   $112.95   $113.00  
  7 purchase totals = $915.15       $1,010.3238   $1,010.33   $1,010.35   $1,010.20