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 $118.91   11.107%   $132.1173   $132.12   $132.10   $132.10  
  Purchase #2 $247.37   5.689%   $261.4429   $261.44   $261.45   $261.40  
  Purchase #3 $207.95   5.785%   $219.9799   $219.98   $220.00   $220.00  
  Purchase #4 $240.41   10.333%   $265.2516   $265.25   $265.25   $265.30  
  Purchase #5 $222.44   8.616%   $241.6054   $241.61   $241.60   $241.60  
  Purchase #6 $61.66   9.686%   $67.6324   $67.63   $67.65   $67.60  
  Purchase #7 $195.67   6.606%   $208.596   $208.60   $208.60   $208.60  
  7 purchase totals = $1,294.41       $1,396.6255   $1,396.63   $1,396.65   $1,396.60