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 $243.37   9.727%   $267.0426   $267.04   $267.05   $267.00  
  Purchase #2 $96.91   8.353%   $105.0049   $105.00   $105.00   $105.00  
  Purchase #3 $14.57   4.867%   $15.2791   $15.28   $15.30   $15.30  
  Purchase #4 $215.82   13.368%   $244.6708   $244.67   $244.65   $244.70  
  Purchase #5 $40.70   9.652%   $44.6284   $44.63   $44.65   $44.60  
  Purchase #6 $39.49   12.254%   $44.3291   $44.33   $44.35   $44.30  
  Purchase #7 $183.25   6.586%   $195.3188   $195.32   $195.30   $195.30  
  7 purchase totals = $834.11       $916.2737   $916.27   $916.30   $916.20