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 $28.73   13.724%   $32.6729   $32.67   $32.65   $32.70  
  Purchase #2 $211.52   6.185%   $224.6025   $224.60   $224.60   $224.60  
  Purchase #3 $57.35   7.648%   $61.7361   $61.74   $61.75   $61.70  
  Purchase #4 $162.37   8.136%   $175.5804   $175.58   $175.60   $175.60  
  Purchase #5 $28.57   7.737%   $30.7805   $30.78   $30.80   $30.80  
  Purchase #6 $92.98   5.550%   $98.1404   $98.14   $98.15   $98.10  
  Purchase #7 $125.87   12.206%   $141.2337   $141.23   $141.25   $141.20  
  7 purchase totals = $707.39       $764.7465   $764.74   $764.80   $764.70