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 $29.84   8.137%   $32.2681   $32.27   $32.25   $32.30  
  Purchase #2 $192.47   6.110%   $204.2299   $204.23   $204.25   $204.20  
  Purchase #3 $87.97   13.749%   $100.065   $100.07   $100.05   $100.10  
  Purchase #4 $56.29   10.649%   $62.2843   $62.28   $62.30   $62.30  
  Purchase #5 $195.56   3.857%   $203.1027   $203.10   $203.10   $203.10  
  Purchase #6 $202.57   3.438%   $209.5344   $209.53   $209.55   $209.50  
  Purchase #7 $13.43   11.598%   $14.9876   $14.99   $15.00   $15.00  
  7 purchase totals = $778.13       $826.4720   $826.47   $826.50   $826.50