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 $204.82   8.383%   $221.9901   $221.99   $222.00   $222.00  
  Purchase #2 $104.97   12.545%   $118.1385   $118.14   $118.15   $118.10  
  Purchase #3 $212.34   4.261%   $221.3878   $221.39   $221.40   $221.40  
  Purchase #4 $215.59   6.812%   $230.276   $230.28   $230.30   $230.30  
  Purchase #5 $249.46   7.779%   $268.8655   $268.87   $268.85   $268.90  
  Purchase #6 $220.44   11.193%   $245.1138   $245.11   $245.10   $245.10  
  Purchase #7 $96.87   7.124%   $103.771   $103.77   $103.75   $103.80  
  7 purchase totals = $1,304.49       $1,409.5427   $1,409.55   $1,409.55   $1,409.60