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 $87.42   12.715%   $98.5355   $98.54   $98.55   $98.50  
  Purchase #2 $223.27   5.751%   $236.1103   $236.11   $236.10   $236.10  
  Purchase #3 $17.57   8.486%   $19.061   $19.06   $19.05   $19.10  
  Purchase #4 $135.29   5.199%   $142.3237   $142.32   $142.30   $142.30  
  Purchase #5 $101.48   10.712%   $112.3505   $112.35   $112.35   $112.40  
  Purchase #6 $187.61   11.533%   $209.2471   $209.25   $209.25   $209.20  
  Purchase #7 $192.43   13.745%   $218.8795   $218.88   $218.90   $218.90  
  7 purchase totals = $945.07       $1,036.5076   $1,036.51   $1,036.50   $1,036.50