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 $247.66   7.271%   $265.6674   $265.67   $265.65   $265.70  
  Purchase #2 $240.47   10.594%   $265.9454   $265.95   $265.95   $265.90  
  Purchase #3 $136.56   9.469%   $149.4909   $149.49   $149.50   $149.50  
  Purchase #4 $130.77   9.857%   $143.66   $143.66   $143.65   $143.70  
  Purchase #5 $200.29   9.136%   $218.5885   $218.59   $218.60   $218.60  
  Purchase #6 $174.40   11.253%   $194.0252   $194.03   $194.05   $194.00  
  Purchase #7 $62.28   4.251%   $64.9275   $64.93   $64.95   $64.90  
  7 purchase totals = $1,192.43       $1,302.3049   $1,302.32   $1,302.35   $1,302.30