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 $183.73   11.372%   $204.6238   $204.62   $204.60   $204.60  
  Purchase #2 $48.87   12.670%   $55.0618   $55.06   $55.05   $55.10  
  Purchase #3 $156.96   7.207%   $168.2721   $168.27   $168.25   $168.30  
  Purchase #4 $56.28   13.248%   $63.736   $63.74   $63.75   $63.70  
  Purchase #5 $103.36   12.497%   $116.2769   $116.28   $116.30   $116.30  
  Purchase #6 $164.66   12.293%   $184.9017   $184.90   $184.90   $184.90  
  Purchase #7 $93.63   7.831%   $100.9622   $100.96   $100.95   $101.00  
  7 purchase totals = $807.49       $893.8345   $893.83   $893.80   $893.90