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 $60.48   11.621%   $67.5084   $67.51   $67.50   $67.50  
  Purchase #2 $132.64   10.169%   $146.1282   $146.13   $146.15   $146.10  
  Purchase #3 $170.55   12.519%   $191.9012   $191.90   $191.90   $191.90  
  Purchase #4 $201.43   6.349%   $214.2188   $214.22   $214.20   $214.20  
  Purchase #5 $6.94   11.612%   $7.7459   $7.75   $7.75   $7.70  
  Purchase #6 $188.41   7.835%   $203.1719   $203.17   $203.15   $203.20  
  Purchase #7 $34.58   7.752%   $37.2606   $37.26   $37.25   $37.30  
  7 purchase totals = $795.03       $867.9350   $867.94   $867.90   $867.90