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 $232.56   10.625%   $257.2695   $257.27   $257.25   $257.30  
  Purchase #2 $34.39   3.626%   $35.637   $35.64   $35.65   $35.60  
  Purchase #3 $238.70   9.799%   $262.0902   $262.09   $262.10   $262.10  
  Purchase #4 $223.57   8.344%   $242.2247   $242.22   $242.20   $242.20  
  Purchase #5 $32.32   5.609%   $34.1328   $34.13   $34.15   $34.10  
  Purchase #6 $92.30   12.623%   $103.951   $103.95   $103.95   $104.00  
  Purchase #7 $41.49   13.222%   $46.9758   $46.98   $47.00   $47.00  
  7 purchase totals = $895.33       $982.2810   $982.28   $982.30   $982.30