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 $72.37   6.119%   $76.7983   $76.80   $76.80   $76.80  
  Purchase #2 $234.73   3.539%   $243.0371   $243.04   $243.05   $243.00  
  Purchase #3 $86.73   5.742%   $91.71   $91.71   $91.70   $91.70  
  Purchase #4 $187.95   4.695%   $196.7743   $196.77   $196.75   $196.80  
  Purchase #5 $192.55   7.282%   $206.5715   $206.57   $206.55   $206.60  
  Purchase #6 $9.29   6.804%   $9.9221   $9.92   $9.90   $9.90  
  Purchase #7 $208.39   10.835%   $230.9691   $230.97   $230.95   $231.00  
  7 purchase totals = $992.01       $1,055.7824   $1,055.78   $1,055.70   $1,055.80