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 $115.25   8.212%   $124.7143   $124.71   $124.70   $124.70  
  Purchase #2 $206.95   12.797%   $233.4334   $233.43   $233.45   $233.40  
  Purchase #3 $187.77   7.720%   $202.2658   $202.27   $202.25   $202.30  
  Purchase #4 $233.72   7.833%   $252.0273   $252.03   $252.05   $252.00  
  Purchase #5 $70.38   12.529%   $79.1979   $79.20   $79.20   $79.20  
  Purchase #6 $60.54   5.792%   $64.0465   $64.05   $64.05   $64.00  
  Purchase #7 $100.28   7.141%   $107.441   $107.44   $107.45   $107.40  
  7 purchase totals = $974.89       $1,063.1262   $1,063.13   $1,063.15   $1,063.00