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 $31.26   5.414%   $32.9524   $32.95   $32.95   $33.00  
  Purchase #2 $226.94   13.204%   $256.9052   $256.91   $256.90   $256.90  
  Purchase #3 $83.66   10.361%   $92.328   $92.33   $92.35   $92.30  
  Purchase #4 $62.33   7.716%   $67.1394   $67.14   $67.15   $67.10  
  Purchase #5 $190.40   12.807%   $214.7845   $214.78   $214.80   $214.80  
  Purchase #6 $228.36   4.363%   $238.3233   $238.32   $238.30   $238.30  
  Purchase #7 $195.32   3.282%   $201.7304   $201.73   $201.75   $201.70  
  7 purchase totals = $1,018.27       $1,104.1632   $1,104.16   $1,104.20   $1,104.10