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 $218.43   12.503%   $245.7403   $245.74   $245.75   $245.70  
  Purchase #2 $94.62   12.598%   $106.5402   $106.54   $106.55   $106.50  
  Purchase #3 $230.29   5.399%   $242.7234   $242.72   $242.70   $242.70  
  Purchase #4 $137.86   6.417%   $146.7065   $146.71   $146.70   $146.70  
  Purchase #5 $241.65   12.349%   $271.4914   $271.49   $271.50   $271.50  
  Purchase #6 $107.25   11.563%   $119.6513   $119.65   $119.65   $119.70  
  Purchase #7 $158.57   10.229%   $174.7901   $174.79   $174.80   $174.80  
  7 purchase totals = $1,188.67       $1,307.6432   $1,307.64   $1,307.65   $1,307.60