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 $115.85   4.744%   $121.3459   $121.35   $121.35   $121.30  
  Purchase #2 $53.64   11.297%   $59.6997   $59.70   $59.70   $59.70  
  Purchase #3 $213.89   11.847%   $239.2295   $239.23   $239.25   $239.20  
  Purchase #4 $250.96   9.841%   $275.657   $275.66   $275.65   $275.70  
  Purchase #5 $101.76   13.748%   $115.75   $115.75   $115.75   $115.80  
  Purchase #6 $55.73   9.113%   $60.8087   $60.81   $60.80   $60.80  
  Purchase #7 $168.79   8.336%   $182.8603   $182.86   $182.85   $182.90  
  7 purchase totals = $960.62       $1,055.3511   $1,055.36   $1,055.35   $1,055.40