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 $239.88   5.869%   $253.9586   $253.96   $253.95   $254.00  
  Purchase #2 $113.36   12.482%   $127.5096   $127.51   $127.50   $127.50  
  Purchase #3 $49.88   4.615%   $52.182   $52.18   $52.20   $52.20  
  Purchase #4 $94.73   12.415%   $106.4907   $106.49   $106.50   $106.50  
  Purchase #5 $244.60   4.312%   $255.1472   $255.15   $255.15   $255.10  
  Purchase #6 $76.43   11.734%   $85.3983   $85.40   $85.40   $85.40  
  Purchase #7 $204.38   8.185%   $221.1085   $221.11   $221.10   $221.10  
  7 purchase totals = $1,023.26       $1,101.7949   $1,101.80   $1,101.80   $1,101.80