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 $32.57   6.652%   $34.7366   $34.74   $34.75   $34.70  
  Purchase #2 $112.92   11.454%   $125.8539   $125.85   $125.85   $125.90  
  Purchase #3 $76.50   4.268%   $79.765   $79.77   $79.75   $79.80  
  Purchase #4 $219.73   7.748%   $236.7547   $236.75   $236.75   $236.80  
  Purchase #5 $156.33   9.419%   $171.0547   $171.05   $171.05   $171.10  
  Purchase #6 $34.44   6.555%   $36.6975   $36.70   $36.70   $36.70  
  Purchase #7 $219.83   12.862%   $248.1045   $248.10   $248.10   $248.10  
  7 purchase totals = $852.32       $932.9669   $932.96   $932.95   $933.10