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 $106.81   12.619%   $120.2884   $120.29   $120.30   $120.30  
  Purchase #2 $135.36   8.561%   $146.9482   $146.95   $146.95   $146.90  
  Purchase #3 $128.33   11.246%   $142.762   $142.76   $142.75   $142.80  
  Purchase #4 $101.71   9.343%   $111.2128   $111.21   $111.20   $111.20  
  Purchase #5 $203.85   5.167%   $214.3829   $214.38   $214.40   $214.40  
  Purchase #6 $83.90   3.586%   $86.9087   $86.91   $86.90   $86.90  
  Purchase #7 $180.36   4.642%   $188.7323   $188.73   $188.75   $188.70  
  7 purchase totals = $940.32       $1,011.2353   $1,011.23   $1,011.25   $1,011.20