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 $118.90   5.234%   $125.1232   $125.12   $125.10   $125.10  
  Purchase #2 $187.91   8.417%   $203.7264   $203.73   $203.75   $203.70  
  Purchase #3 $36.39   4.401%   $37.9915   $37.99   $38.00   $38.00  
  Purchase #4 $70.98   3.662%   $73.5793   $73.58   $73.60   $73.60  
  Purchase #5 $23.75   3.322%   $24.539   $24.54   $24.55   $24.50  
  Purchase #6 $33.47   7.770%   $36.0706   $36.07   $36.05   $36.10  
  Purchase #7 $104.30   3.108%   $107.5416   $107.54   $107.55   $107.50  
  7 purchase totals = $575.70       $608.5716   $608.57   $608.60   $608.50