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 $185.95   10.111%   $204.7514   $204.75   $204.75   $204.80  
  Purchase #2 $73.93   12.239%   $82.9783   $82.98   $83.00   $83.00  
  Purchase #3 $103.37   13.436%   $117.2588   $117.26   $117.25   $117.30  
  Purchase #4 $54.48   11.856%   $60.9391   $60.94   $60.95   $60.90  
  Purchase #5 $13.43   4.248%   $14.0005   $14.00   $14.00   $14.00  
  Purchase #6 $145.84   7.327%   $156.5257   $156.53   $156.55   $156.50  
  Purchase #7 $230.60   13.391%   $261.4796   $261.48   $261.50   $261.50  
  7 purchase totals = $807.60       $897.9334   $897.94   $898.00   $898.00