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 $65.31   4.862%   $68.4854   $68.49   $68.50   $68.50  
  Purchase #2 $182.75   4.695%   $191.3301   $191.33   $191.35   $191.30  
  Purchase #3 $165.63   7.652%   $178.304   $178.30   $178.30   $178.30  
  Purchase #4 $27.48   9.685%   $30.1414   $30.14   $30.15   $30.10  
  Purchase #5 $176.71   13.244%   $200.1135   $200.11   $200.10   $200.10  
  Purchase #6 $63.32   4.665%   $66.2739   $66.27   $66.25   $66.30  
  Purchase #7 $15.74   12.298%   $17.6757   $17.68   $17.70   $17.70  
  7 purchase totals = $696.94       $752.3240   $752.32   $752.35   $752.30