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 $224.31   8.174%   $242.6451   $242.65   $242.65   $242.60  
  Purchase #2 $121.77   3.163%   $125.6216   $125.62   $125.60   $125.60  
  Purchase #3 $83.44   4.248%   $86.9845   $86.98   $87.00   $87.00  
  Purchase #4 $147.57   6.553%   $157.2403   $157.24   $157.25   $157.20  
  Purchase #5 $190.63   10.139%   $209.958   $209.96   $209.95   $210.00  
  Purchase #6 $20.64   3.606%   $21.3843   $21.38   $21.40   $21.40  
  Purchase #7 $173.50   4.303%   $180.9657   $180.97   $180.95   $181.00  
  7 purchase totals = $961.86       $1,024.7995   $1,024.80   $1,024.80   $1,024.80