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 $56.34   4.477%   $58.8623   $58.86   $58.85   $58.90  
  Purchase #2 $204.44   9.857%   $224.5917   $224.59   $224.60   $224.60  
  Purchase #3 $17.32   9.640%   $18.9896   $18.99   $19.00   $19.00  
  Purchase #4 $245.83   4.448%   $256.7645   $256.76   $256.75   $256.80  
  Purchase #5 $115.26   12.556%   $129.732   $129.73   $129.75   $129.70  
  Purchase #6 $157.38   13.320%   $178.343   $178.34   $178.35   $178.30  
  Purchase #7 $65.36   11.189%   $72.6731   $72.67   $72.65   $72.70  
  7 purchase totals = $861.93       $939.9562   $939.94   $939.95   $940.00