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 $245.58   8.218%   $265.7618   $265.76   $265.75   $265.80  
  Purchase #2 $93.32   5.426%   $98.3835   $98.38   $98.40   $98.40  
  Purchase #3 $140.25   10.349%   $154.7645   $154.76   $154.75   $154.80  
  Purchase #4 $241.36   10.242%   $266.0801   $266.08   $266.10   $266.10  
  Purchase #5 $205.65   4.449%   $214.7994   $214.80   $214.80   $214.80  
  Purchase #6 $162.73   4.271%   $169.6802   $169.68   $169.70   $169.70  
  Purchase #7 $57.29   9.581%   $62.779   $62.78   $62.80   $62.80  
  7 purchase totals = $1,146.18       $1,232.2485   $1,232.24   $1,232.30   $1,232.40