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 $32.67   11.144%   $36.3107   $36.31   $36.30   $36.30  
  Purchase #2 $184.91   7.368%   $198.5342   $198.53   $198.55   $198.50  
  Purchase #3 $99.38   12.448%   $111.7508   $111.75   $111.75   $111.80  
  Purchase #4 $126.62   11.592%   $141.2978   $141.30   $141.30   $141.30  
  Purchase #5 $219.95   13.271%   $249.1396   $249.14   $249.15   $249.10  
  Purchase #6 $16.49   10.183%   $18.1692   $18.17   $18.15   $18.20  
  Purchase #7 $68.61   7.661%   $73.8662   $73.87   $73.85   $73.90  
  7 purchase totals = $748.63       $829.0685   $829.07   $829.05   $829.10