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 $59.32   11.433%   $66.1021   $66.10   $66.10   $66.10  
  Purchase #2 $131.91   8.384%   $142.9693   $142.97   $142.95   $143.00  
  Purchase #3 $8.97   10.516%   $9.9133   $9.91   $9.90   $9.90  
  Purchase #4 $236.99   4.567%   $247.8133   $247.81   $247.80   $247.80  
  Purchase #5 $176.40   3.336%   $182.2847   $182.28   $182.30   $182.30  
  Purchase #6 $113.51   5.634%   $119.9052   $119.91   $119.90   $119.90  
  Purchase #7 $228.98   6.268%   $243.3325   $243.33   $243.35   $243.30  
  7 purchase totals = $956.08       $1,012.3204   $1,012.31   $1,012.30   $1,012.30