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 $140.60   4.599%   $147.0662   $147.07   $147.05   $147.10  
  Purchase #2 $197.30   5.602%   $208.3527   $208.35   $208.35   $208.40  
  Purchase #3 $173.40   8.275%   $187.7489   $187.75   $187.75   $187.70  
  Purchase #4 $75.66   4.590%   $79.1328   $79.13   $79.15   $79.10  
  Purchase #5 $178.37   10.826%   $197.6803   $197.68   $197.70   $197.70  
  Purchase #6 $64.33   3.295%   $66.4497   $66.45   $66.45   $66.40  
  Purchase #7 $34.74   6.184%   $36.8883   $36.89   $36.90   $36.90  
  7 purchase totals = $864.40       $923.3189   $923.32   $923.35   $923.30