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 $95.99   5.482%   $101.2522   $101.25   $101.25   $101.30  
  Purchase #2 $18.97   3.402%   $19.6154   $19.62   $19.60   $19.60  
  Purchase #3 $56.84   12.128%   $63.7336   $63.73   $63.75   $63.70  
  Purchase #4 $132.94   10.305%   $146.6395   $146.64   $146.65   $146.60  
  Purchase #5 $33.97   7.819%   $36.6261   $36.63   $36.65   $36.60  
  Purchase #6 $249.40   12.791%   $281.3008   $281.30   $281.30   $281.30  
  Purchase #7 $230.91   6.173%   $245.1641   $245.16   $245.15   $245.20  
  7 purchase totals = $819.02       $894.3317   $894.33   $894.35   $894.30