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 $57.62   9.683%   $63.1993   $63.20   $63.20   $63.20  
  Purchase #2 $133.41   13.351%   $151.2216   $151.22   $151.20   $151.20  
  Purchase #3 $46.61   13.543%   $52.9224   $52.92   $52.90   $52.90  
  Purchase #4 $231.83   3.193%   $239.2323   $239.23   $239.25   $239.20  
  Purchase #5 $23.91   11.814%   $26.7347   $26.73   $26.75   $26.70  
  Purchase #6 $37.38   5.594%   $39.471   $39.47   $39.45   $39.50  
  Purchase #7 $178.90   10.736%   $198.1067   $198.11   $198.10   $198.10  
  7 purchase totals = $709.66       $770.8880   $770.88   $770.85   $770.80