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 $60.84   8.727%   $66.1495   $66.15   $66.15   $66.10  
  Purchase #2 $199.42   13.215%   $225.7734   $225.77   $225.75   $225.80  
  Purchase #3 $84.69   13.260%   $95.9199   $95.92   $95.90   $95.90  
  Purchase #4 $26.78   13.148%   $30.301   $30.30   $30.30   $30.30  
  Purchase #5 $231.42   10.471%   $255.652   $255.65   $255.65   $255.70  
  Purchase #6 $50.26   8.836%   $54.701   $54.70   $54.70   $54.70  
  Purchase #7 $154.71   6.152%   $164.2278   $164.23   $164.25   $164.20  
  7 purchase totals = $808.12       $892.7246   $892.72   $892.70   $892.70