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 $20.75   7.797%   $22.3679   $22.37   $22.35   $22.40  
  Purchase #2 $42.38   3.659%   $43.9307   $43.93   $43.95   $43.90  
  Purchase #3 $178.68   12.864%   $201.6654   $201.67   $201.65   $201.70  
  Purchase #4 $136.64   3.167%   $140.9674   $140.97   $140.95   $141.00  
  Purchase #5 $54.31   13.130%   $61.4409   $61.44   $61.45   $61.40  
  Purchase #6 $139.37   7.493%   $149.813   $149.81   $149.80   $149.80  
  Purchase #7 $14.44   10.254%   $15.9207   $15.92   $15.90   $15.90  
  7 purchase totals = $586.57       $636.1060   $636.11   $636.05   $636.10