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 $218.93   6.530%   $233.2261   $233.23   $233.25   $233.20  
  Purchase #2 $144.38   3.388%   $149.2716   $149.27   $149.25   $149.30  
  Purchase #3 $241.50   12.615%   $271.9652   $271.97   $271.95   $272.00  
  Purchase #4 $243.29   5.581%   $256.868   $256.87   $256.85   $256.90  
  Purchase #5 $213.33   6.456%   $227.1026   $227.10   $227.10   $227.10  
  Purchase #6 $188.65   11.499%   $210.3429   $210.34   $210.35   $210.30  
  Purchase #7 $149.27   5.112%   $156.9007   $156.90   $156.90   $156.90  
  7 purchase totals = $1,399.35       $1,505.6771   $1,505.68   $1,505.65   $1,505.70