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 $235.63   5.645%   $248.9313   $248.93   $248.95   $248.90  
  Purchase #2 $240.66   11.379%   $268.0447   $268.04   $268.05   $268.00  
  Purchase #3 $196.78   9.681%   $215.8303   $215.83   $215.85   $215.80  
  Purchase #4 $99.47   7.214%   $106.6458   $106.65   $106.65   $106.60  
  Purchase #5 $198.86   8.467%   $215.6975   $215.70   $215.70   $215.70  
  Purchase #6 $136.90   6.431%   $145.704   $145.70   $145.70   $145.70  
  Purchase #7 $65.56   5.182%   $68.9573   $68.96   $68.95   $69.00  
  7 purchase totals = $1,173.86       $1,269.8109   $1,269.81   $1,269.85   $1,269.70