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 $63.43   12.526%   $71.3752   $71.38   $71.40   $71.40  
  Purchase #2 $29.34   6.790%   $31.3322   $31.33   $31.35   $31.30  
  Purchase #3 $101.90   7.265%   $109.303   $109.30   $109.30   $109.30  
  Purchase #4 $243.93   4.694%   $255.3801   $255.38   $255.40   $255.40  
  Purchase #5 $241.29   8.184%   $261.0372   $261.04   $261.05   $261.00  
  Purchase #6 $21.28   11.556%   $23.7391   $23.74   $23.75   $23.70  
  Purchase #7 $200.65   6.207%   $213.1043   $213.10   $213.10   $213.10  
  7 purchase totals = $901.82       $965.2711   $965.27   $965.35   $965.20