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 $76.62   10.671%   $84.7961   $84.80   $84.80   $84.80  
  Purchase #2 $166.78   8.545%   $181.0314   $181.03   $181.05   $181.00  
  Purchase #3 $178.99   6.575%   $190.7586   $190.76   $190.75   $190.80  
  Purchase #4 $226.44   10.217%   $249.5754   $249.58   $249.60   $249.60  
  Purchase #5 $14.57   3.431%   $15.0699   $15.07   $15.05   $15.10  
  Purchase #6 $29.99   9.183%   $32.744   $32.74   $32.75   $32.70  
  Purchase #7 $55.49   11.366%   $61.797   $61.80   $61.80   $61.80  
  7 purchase totals = $748.88       $815.7724   $815.78   $815.80   $815.80