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 $240.26   7.514%   $258.3131   $258.31   $258.30   $258.30  
  Purchase #2 $247.57   6.519%   $263.7091   $263.71   $263.70   $263.70  
  Purchase #3 $32.32   13.572%   $36.7065   $36.71   $36.70   $36.70  
  Purchase #4 $226.76   7.619%   $244.0368   $244.04   $244.05   $244.00  
  Purchase #5 $198.95   4.478%   $207.859   $207.86   $207.85   $207.90  
  Purchase #6 $188.79   10.133%   $207.9201   $207.92   $207.90   $207.90  
  Purchase #7 $218.75   7.292%   $234.7013   $234.70   $234.70   $234.70  
  7 purchase totals = $1,353.40       $1,453.2459   $1,453.25   $1,453.20   $1,453.20