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 $92.27   6.284%   $98.0682   $98.07   $98.05   $98.10  
  Purchase #2 $122.78   6.618%   $130.9056   $130.91   $130.90   $130.90  
  Purchase #3 $145.51   6.187%   $154.5127   $154.51   $154.50   $154.50  
  Purchase #4 $63.60   13.404%   $72.1249   $72.12   $72.10   $72.10  
  Purchase #5 $25.66   4.282%   $26.7588   $26.76   $26.75   $26.80  
  Purchase #6 $131.64   4.526%   $137.598   $137.60   $137.60   $137.60  
  Purchase #7 $68.39   10.194%   $75.3617   $75.36   $75.35   $75.40  
  7 purchase totals = $649.85       $695.3299   $695.33   $695.25   $695.40