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 $226.44   5.644%   $239.2203   $239.22   $239.20   $239.20  
  Purchase #2 $12.44   3.413%   $12.8646   $12.86   $12.85   $12.90  
  Purchase #3 $158.27   6.251%   $168.1635   $168.16   $168.15   $168.20  
  Purchase #4 $236.77   10.613%   $261.8984   $261.90   $261.90   $261.90  
  Purchase #5 $218.61   11.241%   $243.184   $243.18   $243.20   $243.20  
  Purchase #6 $49.92   8.774%   $54.3   $54.30   $54.30   $54.30  
  Purchase #7 $182.64   9.529%   $200.0438   $200.04   $200.05   $200.00  
  7 purchase totals = $1,085.09       $1,179.6746   $1,179.66   $1,179.65   $1,179.70