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 $214.74   5.849%   $227.3001   $227.30   $227.30   $227.30  
  Purchase #2 $196.28   3.763%   $203.666   $203.67   $203.65   $203.70  
  Purchase #3 $74.49   4.689%   $77.9828   $77.98   $78.00   $78.00  
  Purchase #4 $100.76   11.852%   $112.7021   $112.70   $112.70   $112.70  
  Purchase #5 $59.87   7.654%   $64.4524   $64.45   $64.45   $64.50  
  Purchase #6 $66.68   11.179%   $74.1342   $74.13   $74.15   $74.10  
  Purchase #7 $173.72   13.707%   $197.5318   $197.53   $197.55   $197.50  
  7 purchase totals = $886.54       $957.7694   $957.76   $957.80   $957.80