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 $199.57   3.186%   $205.9283   $205.93   $205.95   $205.90  
  Purchase #2 $214.44   12.362%   $240.9491   $240.95   $240.95   $240.90  
  Purchase #3 $15.70   11.758%   $17.546   $17.55   $17.55   $17.50  
  Purchase #4 $6.79   5.289%   $7.1491   $7.15   $7.15   $7.10  
  Purchase #5 $144.36   8.334%   $156.391   $156.39   $156.40   $156.40  
  Purchase #6 $190.32   8.385%   $206.2783   $206.28   $206.30   $206.30  
  Purchase #7 $205.34   7.157%   $220.0362   $220.04   $220.05   $220.00  
  7 purchase totals = $976.52       $1,054.2780   $1,054.29   $1,054.35   $1,054.10