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 $47.69   8.362%   $51.6778   $51.68   $51.70   $51.70  
  Purchase #2 $247.74   8.404%   $268.5601   $268.56   $268.55   $268.60  
  Purchase #3 $209.61   10.727%   $232.0949   $232.09   $232.10   $232.10  
  Purchase #4 $198.43   3.103%   $204.5873   $204.59   $204.60   $204.60  
  Purchase #5 $54.49   4.665%   $57.032   $57.03   $57.05   $57.00  
  Purchase #6 $247.93   8.454%   $268.89   $268.89   $268.90   $268.90  
  Purchase #7 $130.61   10.505%   $144.3306   $144.33   $144.35   $144.30  
  7 purchase totals = $1,136.50       $1,227.1727   $1,227.17   $1,227.25   $1,227.20