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 $22.71   4.744%   $23.7874   $23.79   $23.80   $23.80  
  Purchase #2 $137.50   12.455%   $154.6256   $154.63   $154.65   $154.60  
  Purchase #3 $167.80   9.441%   $183.642   $183.64   $183.65   $183.60  
  Purchase #4 $118.93   12.236%   $133.4823   $133.48   $133.50   $133.50  
  Purchase #5 $245.81   8.727%   $267.2618   $267.26   $267.25   $267.30  
  Purchase #6 $184.66   3.773%   $191.6272   $191.63   $191.65   $191.60  
  Purchase #7 $191.45   7.131%   $205.1023   $205.10   $205.10   $205.10  
  7 purchase totals = $1,068.86       $1,159.5286   $1,159.53   $1,159.60   $1,159.50