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 $194.81   9.621%   $213.5527   $213.55   $213.55   $213.60  
  Purchase #2 $59.42   8.251%   $64.3227   $64.32   $64.30   $64.30  
  Purchase #3 $226.45   8.285%   $245.2114   $245.21   $245.20   $245.20  
  Purchase #4 $196.32   5.686%   $207.4828   $207.48   $207.50   $207.50  
  Purchase #5 $10.40   9.416%   $11.3793   $11.38   $11.40   $11.40  
  Purchase #6 $175.63   9.725%   $192.71   $192.71   $192.70   $192.70  
  Purchase #7 $92.40   7.747%   $99.5582   $99.56   $99.55   $99.60  
  7 purchase totals = $955.43       $1,034.2171   $1,034.21   $1,034.20   $1,034.30