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 $81.48   8.532%   $88.4319   $88.43   $88.45   $88.40  
  Purchase #2 $169.49   10.696%   $187.6187   $187.62   $187.60   $187.60  
  Purchase #3 $231.96   11.670%   $259.0297   $259.03   $259.05   $259.00  
  Purchase #4 $248.83   9.782%   $273.1706   $273.17   $273.15   $273.20  
  Purchase #5 $233.60   7.184%   $250.3818   $250.38   $250.40   $250.40  
  Purchase #6 $93.74   5.725%   $99.1066   $99.11   $99.10   $99.10  
  Purchase #7 $101.92   10.348%   $112.4667   $112.47   $112.45   $112.50  
  7 purchase totals = $1,161.02       $1,270.2060   $1,270.21   $1,270.20   $1,270.20