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 $179.66   8.657%   $195.2132   $195.21   $195.20   $195.20  
  Purchase #2 $122.95   5.199%   $129.3422   $129.34   $129.35   $129.30  
  Purchase #3 $215.98   8.323%   $233.956   $233.96   $233.95   $234.00  
  Purchase #4 $93.49   12.525%   $105.1996   $105.20   $105.20   $105.20  
  Purchase #5 $241.29   3.594%   $249.962   $249.96   $249.95   $250.00  
  Purchase #6 $206.95   3.871%   $214.961   $214.96   $214.95   $215.00  
  Purchase #7 $158.86   5.500%   $167.5973   $167.60   $167.60   $167.60  
  7 purchase totals = $1,219.18       $1,296.2313   $1,296.23   $1,296.20   $1,296.30