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 $225.94   6.662%   $240.9921   $240.99   $241.00   $241.00  
  Purchase #2 $68.40   12.796%   $77.1525   $77.15   $77.15   $77.20  
  Purchase #3 $192.48   10.544%   $212.7751   $212.78   $212.80   $212.80  
  Purchase #4 $192.73   13.262%   $218.2899   $218.29   $218.30   $218.30  
  Purchase #5 $41.42   5.763%   $43.807   $43.81   $43.80   $43.80  
  Purchase #6 $155.63   11.460%   $173.4652   $173.47   $173.45   $173.50  
  Purchase #7 $52.43   7.464%   $56.3434   $56.34   $56.35   $56.30  
  7 purchase totals = $929.03       $1,022.8252   $1,022.83   $1,022.85   $1,022.90