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 $62.39   6.852%   $66.665   $66.67   $66.65   $66.70  
  Purchase #2 $181.59   3.575%   $188.0818   $188.08   $188.10   $188.10  
  Purchase #3 $231.49   8.544%   $251.2685   $251.27   $251.25   $251.30  
  Purchase #4 $176.85   11.379%   $196.9738   $196.97   $196.95   $197.00  
  Purchase #5 $185.83   9.727%   $203.9057   $203.91   $203.90   $203.90  
  Purchase #6 $38.30   9.504%   $41.94   $41.94   $41.95   $41.90  
  Purchase #7 $7.30   7.580%   $7.8533   $7.85   $7.85   $7.90  
  7 purchase totals = $883.75       $956.6881   $956.69   $956.65   $956.80