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 $213.26   6.585%   $227.3032   $227.30   $227.30   $227.30  
  Purchase #2 $241.83   12.145%   $271.2003   $271.20   $271.20   $271.20  
  Purchase #3 $109.56   7.561%   $117.8438   $117.84   $117.85   $117.80  
  Purchase #4 $249.53   5.383%   $262.9622   $262.96   $262.95   $263.00  
  Purchase #5 $59.64   7.598%   $64.1714   $64.17   $64.15   $64.20  
  Purchase #6 $43.86   9.779%   $48.1491   $48.15   $48.15   $48.10  
  Purchase #7 $204.74   9.210%   $223.5966   $223.60   $223.60   $223.60  
  7 purchase totals = $1,122.42       $1,215.2266   $1,215.22   $1,215.20   $1,215.20