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 $67.34   5.357%   $70.9474   $70.95   $70.95   $70.90  
  Purchase #2 $141.74   3.642%   $146.9022   $146.90   $146.90   $146.90  
  Purchase #3 $112.60   13.210%   $127.4745   $127.47   $127.45   $127.50  
  Purchase #4 $158.96   11.243%   $176.8319   $176.83   $176.85   $176.80  
  Purchase #5 $148.82   4.619%   $155.694   $155.69   $155.70   $155.70  
  Purchase #6 $229.95   7.672%   $247.5918   $247.59   $247.60   $247.60  
  Purchase #7 $182.84   7.309%   $196.2038   $196.20   $196.20   $196.20  
  7 purchase totals = $1,042.25       $1,121.6456   $1,121.63   $1,121.65   $1,121.60