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 $214.62   12.663%   $241.7973   $241.80   $241.80   $241.80  
  Purchase #2 $8.61   9.219%   $9.4038   $9.40   $9.40   $9.40  
  Purchase #3 $74.78   3.219%   $77.1872   $77.19   $77.20   $77.20  
  Purchase #4 $41.47   11.759%   $46.3465   $46.35   $46.35   $46.30  
  Purchase #5 $162.34   12.690%   $182.9409   $182.94   $182.95   $182.90  
  Purchase #6 $65.40   3.484%   $67.6785   $67.68   $67.70   $67.70  
  Purchase #7 $213.80   12.121%   $239.7147   $239.71   $239.70   $239.70  
  7 purchase totals = $781.02       $865.0689   $865.07   $865.10   $865.00