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 $242.63   8.530%   $263.3263   $263.33   $263.35   $263.30  
  Purchase #2 $88.53   5.514%   $93.4115   $93.41   $93.40   $93.40  
  Purchase #3 $170.76   12.819%   $192.6497   $192.65   $192.65   $192.60  
  Purchase #4 $56.43   10.830%   $62.5414   $62.54   $62.55   $62.50  
  Purchase #5 $24.26   4.163%   $25.2699   $25.27   $25.25   $25.30  
  Purchase #6 $192.69   3.109%   $198.6807   $198.68   $198.70   $198.70  
  Purchase #7 $119.65   9.117%   $130.5585   $130.56   $130.55   $130.60  
  7 purchase totals = $894.95       $966.4380   $966.44   $966.45   $966.40