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 $91.33   4.173%   $95.1412   $95.14   $95.15   $95.10  
  Purchase #2 $12.97   10.306%   $14.3067   $14.31   $14.30   $14.30  
  Purchase #3 $67.73   7.743%   $72.9743   $72.97   $72.95   $73.00  
  Purchase #4 $97.36   6.194%   $103.3905   $103.39   $103.40   $103.40  
  Purchase #5 $163.31   11.448%   $182.0057   $182.01   $182.00   $182.00  
  Purchase #6 $236.30   3.568%   $244.7312   $244.73   $244.75   $244.70  
  Purchase #7 $8.48   9.669%   $9.2999   $9.30   $9.30   $9.30  
  7 purchase totals = $677.48       $721.8495   $721.85   $721.85   $721.80