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 $86.98   13.725%   $98.918   $98.92   $98.90   $98.90  
  Purchase #2 $71.27   8.256%   $77.1541   $77.15   $77.15   $77.20  
  Purchase #3 $217.55   9.264%   $237.7038   $237.70   $237.70   $237.70  
  Purchase #4 $192.82   11.268%   $214.547   $214.55   $214.55   $214.50  
  Purchase #5 $125.54   12.251%   $140.9199   $140.92   $140.90   $140.90  
  Purchase #6 $224.74   5.555%   $237.2243   $237.22   $237.20   $237.20  
  Purchase #7 $59.55   4.327%   $62.1267   $62.13   $62.15   $62.10  
  7 purchase totals = $978.45       $1,068.5938   $1,068.59   $1,068.55   $1,068.50