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 $211.27   13.362%   $239.4999   $239.50   $239.50   $239.50  
  Purchase #2 $152.91   3.767%   $158.6701   $158.67   $158.65   $158.70  
  Purchase #3 $133.66   6.842%   $142.805   $142.81   $142.80   $142.80  
  Purchase #4 $227.25   3.166%   $234.4447   $234.44   $234.45   $234.40  
  Purchase #5 $203.34   5.679%   $214.8877   $214.89   $214.90   $214.90  
  Purchase #6 $170.89   12.393%   $192.0684   $192.07   $192.05   $192.10  
  Purchase #7 $215.87   8.386%   $233.9729   $233.97   $233.95   $234.00  
  7 purchase totals = $1,315.19       $1,416.3487   $1,416.35   $1,416.30   $1,416.40