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 $64.81   13.220%   $73.3779   $73.38   $73.40   $73.40  
  Purchase #2 $204.25   13.314%   $231.4438   $231.44   $231.45   $231.40  
  Purchase #3 $169.66   4.607%   $177.4762   $177.48   $177.50   $177.50  
  Purchase #4 $199.57   8.496%   $216.5255   $216.53   $216.55   $216.50  
  Purchase #5 $51.43   7.657%   $55.368   $55.37   $55.35   $55.40  
  Purchase #6 $234.99   9.198%   $256.6044   $256.60   $256.60   $256.60  
  Purchase #7 $94.88   8.762%   $103.1934   $103.19   $103.20   $103.20  
  7 purchase totals = $1,019.59       $1,113.9892   $1,113.99   $1,114.05   $1,114.00