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 $66.37   10.860%   $73.5778   $73.58   $73.60   $73.60  
  Purchase #2 $178.39   5.740%   $188.6296   $188.63   $188.65   $188.60  
  Purchase #3 $61.53   3.194%   $63.4953   $63.50   $63.50   $63.50  
  Purchase #4 $111.27   12.136%   $124.7737   $124.77   $124.75   $124.80  
  Purchase #5 $121.58   3.160%   $125.4219   $125.42   $125.40   $125.40  
  Purchase #6 $168.85   3.529%   $174.8087   $174.81   $174.80   $174.80  
  Purchase #7 $39.37   10.334%   $43.4385   $43.44   $43.45   $43.40  
  7 purchase totals = $747.36       $794.1455   $794.15   $794.15   $794.10