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 $200.72   12.109%   $225.0252   $225.03   $225.05   $225.00  
  Purchase #2 $105.43   3.291%   $108.8997   $108.90   $108.90   $108.90  
  Purchase #3 $69.67   9.518%   $76.3012   $76.30   $76.30   $76.30  
  Purchase #4 $227.54   6.271%   $241.809   $241.81   $241.80   $241.80  
  Purchase #5 $129.87   5.325%   $136.7856   $136.79   $136.80   $136.80  
  Purchase #6 $26.32   5.670%   $27.8123   $27.81   $27.80   $27.80  
  Purchase #7 $214.99   7.606%   $231.3421   $231.34   $231.35   $231.30  
  7 purchase totals = $974.54       $1,047.9751   $1,047.98   $1,048.00   $1,047.90