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 $54.92   11.767%   $61.3824   $61.38   $61.40   $61.40  
  Purchase #2 $129.85   12.412%   $145.967   $145.97   $145.95   $146.00  
  Purchase #3 $193.80   10.561%   $214.2672   $214.27   $214.25   $214.30  
  Purchase #4 $246.41   13.188%   $278.9066   $278.91   $278.90   $278.90  
  Purchase #5 $43.50   8.124%   $47.0339   $47.03   $47.05   $47.00  
  Purchase #6 $81.94   6.392%   $87.1776   $87.18   $87.20   $87.20  
  Purchase #7 $169.67   5.743%   $179.4141   $179.41   $179.40   $179.40  
  7 purchase totals = $920.09       $1,014.1488   $1,014.15   $1,014.15   $1,014.20