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 $76.69   10.323%   $84.6067   $84.61   $84.60   $84.60  
  Purchase #2 $58.30   12.640%   $65.6691   $65.67   $65.65   $65.70  
  Purchase #3 $209.73   7.802%   $226.0931   $226.09   $226.10   $226.10  
  Purchase #4 $13.68   6.318%   $14.5443   $14.54   $14.55   $14.50  
  Purchase #5 $162.87   8.808%   $177.2156   $177.22   $177.20   $177.20  
  Purchase #6 $192.47   13.445%   $218.3476   $218.35   $218.35   $218.30  
  Purchase #7 $215.35   5.433%   $227.05   $227.05   $227.05   $227.10  
  7 purchase totals = $929.09       $1,013.5264   $1,013.53   $1,013.50   $1,013.50