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 $98.84   8.228%   $106.9726   $106.97   $106.95   $107.00  
  Purchase #2 $168.39   13.258%   $190.7151   $190.72   $190.70   $190.70  
  Purchase #3 $149.64   3.179%   $154.3971   $154.40   $154.40   $154.40  
  Purchase #4 $72.27   8.138%   $78.1513   $78.15   $78.15   $78.20  
  Purchase #5 $94.92   9.598%   $104.0304   $104.03   $104.05   $104.00  
  Purchase #6 $211.71   4.712%   $221.6858   $221.69   $221.70   $221.70  
  Purchase #7 $111.50   7.340%   $119.6841   $119.68   $119.70   $119.70  
  7 purchase totals = $907.27       $975.6364   $975.64   $975.65   $975.70