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 $208.99   13.373%   $236.9382   $236.94   $236.95   $236.90  
  Purchase #2 $119.88   12.254%   $134.5701   $134.57   $134.55   $134.60  
  Purchase #3 $88.82   8.362%   $96.2471   $96.25   $96.25   $96.20  
  Purchase #4 $19.70   11.465%   $21.9586   $21.96   $21.95   $22.00  
  Purchase #5 $60.41   3.190%   $62.3371   $62.34   $62.35   $62.30  
  Purchase #6 $176.60   11.409%   $196.7483   $196.75   $196.75   $196.70  
  Purchase #7 $233.69   10.825%   $258.9869   $258.99   $259.00   $259.00  
  7 purchase totals = $908.09       $1,007.7863   $1,007.80   $1,007.80   $1,007.70