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 $191.34   4.291%   $199.5504   $199.55   $199.55   $199.60  
  Purchase #2 $202.57   6.735%   $216.2131   $216.21   $216.20   $216.20  
  Purchase #3 $206.28   11.835%   $230.6932   $230.69   $230.70   $230.70  
  Purchase #4 $215.96   3.731%   $224.0175   $224.02   $224.00   $224.00  
  Purchase #5 $41.78   11.776%   $46.7   $46.70   $46.70   $46.70  
  Purchase #6 $21.56   7.314%   $23.1369   $23.14   $23.15   $23.10  
  Purchase #7 $53.86   10.261%   $59.3866   $59.39   $59.40   $59.40  
  7 purchase totals = $933.35       $999.6977   $999.70   $999.70   $999.70