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 $7.75   9.296%   $8.4704   $8.47   $8.45   $8.50  
  Purchase #2 $170.97   10.215%   $188.4346   $188.43   $188.45   $188.40  
  Purchase #3 $57.51   4.854%   $60.3015   $60.30   $60.30   $60.30  
  Purchase #4 $246.57   13.275%   $279.3022   $279.30   $279.30   $279.30  
  Purchase #5 $104.26   6.432%   $110.966   $110.97   $110.95   $111.00  
  Purchase #6 $61.78   4.544%   $64.5873   $64.59   $64.60   $64.60  
  Purchase #7 $233.70   4.359%   $243.887   $243.89   $243.90   $243.90  
  7 purchase totals = $882.54       $955.9490   $955.95   $955.95   $956.00