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 $118.83   10.248%   $131.0077   $131.01   $131.00   $131.00  
  Purchase #2 $123.27   8.390%   $133.6124   $133.61   $133.60   $133.60  
  Purchase #3 $239.52   13.550%   $271.975   $271.98   $272.00   $272.00  
  Purchase #4 $210.63   10.790%   $233.357   $233.36   $233.35   $233.40  
  Purchase #5 $78.44   8.251%   $84.9121   $84.91   $84.90   $84.90  
  Purchase #6 $187.33   10.332%   $206.6849   $206.68   $206.70   $206.70  
  Purchase #7 $227.79   13.333%   $258.1612   $258.16   $258.15   $258.20  
  7 purchase totals = $1,185.81       $1,319.7103   $1,319.71   $1,319.70   $1,319.80