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 $85.35   12.582%   $96.0887   $96.09   $96.10   $96.10  
  Purchase #2 $54.47   6.224%   $57.8602   $57.86   $57.85   $57.90  
  Purchase #3 $195.73   9.665%   $214.6473   $214.65   $214.65   $214.60  
  Purchase #4 $70.34   10.701%   $77.8671   $77.87   $77.85   $77.90  
  Purchase #5 $14.76   5.783%   $15.6136   $15.61   $15.60   $15.60  
  Purchase #6 $89.40   4.647%   $93.5544   $93.55   $93.55   $93.60  
  Purchase #7 $151.57   12.688%   $170.8012   $170.80   $170.80   $170.80  
  7 purchase totals = $661.62       $726.4325   $726.43   $726.40   $726.50