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 $191.37   12.598%   $215.4788   $215.48   $215.50   $215.50  
  Purchase #2 $62.47   5.555%   $65.9402   $65.94   $65.95   $65.90  
  Purchase #3 $154.59   7.159%   $165.6571   $165.66   $165.65   $165.70  
  Purchase #4 $58.42   8.331%   $63.287   $63.29   $63.30   $63.30  
  Purchase #5 $157.25   3.277%   $162.4031   $162.40   $162.40   $162.40  
  Purchase #6 $5.89   12.119%   $6.6038   $6.60   $6.60   $6.60  
  Purchase #7 $63.36   10.127%   $69.7765   $69.78   $69.80   $69.80  
  7 purchase totals = $693.35       $749.1465   $749.15   $749.20   $749.20