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 $222.98   13.659%   $253.4368   $253.44   $253.45   $253.40  
  Purchase #2 $239.84   9.620%   $262.9126   $262.91   $262.90   $262.90  
  Purchase #3 $98.91   11.826%   $110.6071   $110.61   $110.60   $110.60  
  Purchase #4 $169.69   10.413%   $187.3598   $187.36   $187.35   $187.40  
  Purchase #5 $124.67   9.388%   $136.374   $136.37   $136.35   $136.40  
  Purchase #6 $221.60   4.518%   $231.6119   $231.61   $231.60   $231.60  
  Purchase #7 $33.44   8.691%   $36.3463   $36.35   $36.35   $36.30  
  7 purchase totals = $1,111.13       $1,218.6485   $1,218.65   $1,218.60   $1,218.60