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 $202.75   6.671%   $216.2755   $216.28   $216.30   $216.30  
  Purchase #2 $51.89   6.787%   $55.4118   $55.41   $55.40   $55.40  
  Purchase #3 $184.51   4.601%   $192.9993   $193.00   $193.00   $193.00  
  Purchase #4 $168.69   9.321%   $184.4136   $184.41   $184.40   $184.40  
  Purchase #5 $146.55   11.132%   $162.8639   $162.86   $162.85   $162.90  
  Purchase #6 $112.40   4.763%   $117.7536   $117.75   $117.75   $117.80  
  Purchase #7 $176.57   9.855%   $193.971   $193.97   $193.95   $194.00  
  7 purchase totals = $1,043.36       $1,123.6887   $1,123.68   $1,123.65   $1,123.80