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 $57.97   3.744%   $60.1404   $60.14   $60.15   $60.10  
  Purchase #2 $171.49   3.611%   $177.6825   $177.68   $177.70   $177.70  
  Purchase #3 $221.88   12.625%   $249.8924   $249.89   $249.90   $249.90  
  Purchase #4 $230.29   8.733%   $250.4012   $250.40   $250.40   $250.40  
  Purchase #5 $199.72   3.578%   $206.866   $206.87   $206.85   $206.90  
  Purchase #6 $88.44   10.762%   $97.9579   $97.96   $97.95   $98.00  
  Purchase #7 $133.62   12.271%   $150.0165   $150.02   $150.00   $150.00  
  7 purchase totals = $1,103.41       $1,192.9569   $1,192.96   $1,192.95   $1,193.00