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 $192.69   8.603%   $209.2671   $209.27   $209.25   $209.30  
  Purchase #2 $51.70   3.356%   $53.4351   $53.44   $53.45   $53.40  
  Purchase #3 $245.85   8.519%   $266.794   $266.79   $266.80   $266.80  
  Purchase #4 $100.40   6.362%   $106.7874   $106.79   $106.80   $106.80  
  Purchase #5 $98.99   8.230%   $107.1369   $107.14   $107.15   $107.10  
  Purchase #6 $100.79   4.299%   $105.123   $105.12   $105.10   $105.10  
  Purchase #7 $217.47   4.116%   $226.4211   $226.42   $226.40   $226.40  
  7 purchase totals = $1,007.89       $1,074.9646   $1,074.97   $1,074.95   $1,074.90