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 $244.74   6.819%   $261.4288   $261.43   $261.45   $261.40  
  Purchase #2 $58.38   10.152%   $64.3067   $64.31   $64.30   $64.30  
  Purchase #3 $135.34   8.853%   $147.3217   $147.32   $147.30   $147.30  
  Purchase #4 $101.87   5.574%   $107.5482   $107.55   $107.55   $107.50  
  Purchase #5 $190.55   12.350%   $214.0829   $214.08   $214.10   $214.10  
  Purchase #6 $212.87   11.292%   $236.9073   $236.91   $236.90   $236.90  
  Purchase #7 $131.77   9.792%   $144.6729   $144.67   $144.65   $144.70  
  7 purchase totals = $1,075.52       $1,176.2685   $1,176.27   $1,176.25   $1,176.20