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 $180.61   10.306%   $199.2237   $199.22   $199.20   $199.20  
  Purchase #2 $216.99   13.631%   $246.5679   $246.57   $246.55   $246.60  
  Purchase #3 $173.43   4.447%   $181.1424   $181.14   $181.15   $181.10  
  Purchase #4 $122.99   13.228%   $139.2591   $139.26   $139.25   $139.30  
  Purchase #5 $19.41   5.280%   $20.4348   $20.43   $20.45   $20.40  
  Purchase #6 $79.94   8.615%   $86.8268   $86.83   $86.85   $86.80  
  Purchase #7 $91.54   5.127%   $96.2333   $96.23   $96.25   $96.20  
  7 purchase totals = $884.91       $969.6880   $969.68   $969.70   $969.60