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 $61.27   9.728%   $67.2303   $67.23   $67.25   $67.20  
  Purchase #2 $105.99   10.233%   $116.836   $116.84   $116.85   $116.80  
  Purchase #3 $151.54   8.224%   $164.0026   $164.00   $164.00   $164.00  
  Purchase #4 $224.60   3.168%   $231.7153   $231.72   $231.70   $231.70  
  Purchase #5 $176.92   13.311%   $200.4698   $200.47   $200.45   $200.50  
  Purchase #6 $233.65   9.298%   $255.3748   $255.37   $255.35   $255.40  
  Purchase #7 $174.73   6.536%   $186.1504   $186.15   $186.15   $186.20  
  7 purchase totals = $1,128.70       $1,221.7792   $1,221.78   $1,221.75   $1,221.80