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 $196.25   4.323%   $204.7339   $204.73   $204.75   $204.70  
  Purchase #2 $162.75   13.520%   $184.7538   $184.75   $184.75   $184.80  
  Purchase #3 $231.56   3.573%   $239.8336   $239.83   $239.85   $239.80  
  Purchase #4 $72.28   10.210%   $79.6598   $79.66   $79.65   $79.70  
  Purchase #5 $112.40   12.254%   $126.1735   $126.17   $126.15   $126.20  
  Purchase #6 $247.49   6.437%   $263.4209   $263.42   $263.40   $263.40  
  Purchase #7 $240.73   3.796%   $249.8681   $249.87   $249.85   $249.90  
  7 purchase totals = $1,263.46       $1,348.4436   $1,348.43   $1,348.40   $1,348.50