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 $6.44   10.800%   $7.1355   $7.14   $7.15   $7.10  
  Purchase #2 $226.30   11.741%   $252.8699   $252.87   $252.85   $252.90  
  Purchase #3 $217.33   4.694%   $227.5315   $227.53   $227.55   $227.50  
  Purchase #4 $189.62   8.259%   $205.2807   $205.28   $205.30   $205.30  
  Purchase #5 $97.72   11.353%   $108.8142   $108.81   $108.80   $108.80  
  Purchase #6 $9.31   12.353%   $10.4601   $10.46   $10.45   $10.50  
  Purchase #7 $69.78   3.719%   $72.3751   $72.38   $72.40   $72.40  
  7 purchase totals = $816.50       $884.4670   $884.47   $884.50   $884.50