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 $114.32   10.660%   $126.5065   $126.51   $126.50   $126.50  
  Purchase #2 $97.39   3.819%   $101.1093   $101.11   $101.10   $101.10  
  Purchase #3 $71.57   6.283%   $76.0667   $76.07   $76.05   $76.10  
  Purchase #4 $56.31   3.368%   $58.2065   $58.21   $58.20   $58.20  
  Purchase #5 $194.68   12.809%   $219.6166   $219.62   $219.60   $219.60  
  Purchase #6 $222.75   11.287%   $247.8918   $247.89   $247.90   $247.90  
  Purchase #7 $20.48   3.553%   $21.2077   $21.21   $21.20   $21.20  
  7 purchase totals = $777.50       $850.6051   $850.62   $850.55   $850.60