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 $225.49   13.424%   $255.7598   $255.76   $255.75   $255.80  
  Purchase #2 $209.64   4.298%   $218.6503   $218.65   $218.65   $218.70  
  Purchase #3 $168.42   3.117%   $173.6697   $173.67   $173.65   $173.70  
  Purchase #4 $105.30   12.842%   $118.8226   $118.82   $118.80   $118.80  
  Purchase #5 $178.52   12.181%   $200.2655   $200.27   $200.25   $200.30  
  Purchase #6 $143.77   12.701%   $162.0302   $162.03   $162.05   $162.00  
  Purchase #7 $70.51   4.328%   $73.5617   $73.56   $73.55   $73.60  
  7 purchase totals = $1,101.65       $1,202.7598   $1,202.76   $1,202.70   $1,202.90