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 $29.89   3.540%   $30.9481   $30.95   $30.95   $30.90  
  Purchase #2 $27.98   11.739%   $31.2646   $31.26   $31.25   $31.30  
  Purchase #3 $30.36   4.190%   $31.6321   $31.63   $31.65   $31.60  
  Purchase #4 $18.72   7.341%   $20.0942   $20.09   $20.10   $20.10  
  Purchase #5 $162.47   11.645%   $181.3896   $181.39   $181.40   $181.40  
  Purchase #6 $156.98   8.445%   $170.237   $170.24   $170.25   $170.20  
  Purchase #7 $182.43   9.579%   $199.905   $199.91   $199.90   $199.90  
  7 purchase totals = $608.83       $665.4706   $665.47   $665.50   $665.40