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 $209.29   5.771%   $221.3681   $221.37   $221.35   $221.40  
  Purchase #2 $240.55   10.712%   $266.3177   $266.32   $266.30   $266.30  
  Purchase #3 $235.25   5.152%   $247.3701   $247.37   $247.35   $247.40  
  Purchase #4 $112.83   5.767%   $119.3369   $119.34   $119.35   $119.30  
  Purchase #5 $95.81   3.211%   $98.8865   $98.89   $98.90   $98.90  
  Purchase #6 $223.84   13.206%   $253.4003   $253.40   $253.40   $253.40  
  Purchase #7 $250.65   10.103%   $275.9732   $275.97   $275.95   $276.00  
  7 purchase totals = $1,368.22       $1,482.6528   $1,482.66   $1,482.60   $1,482.70