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 $246.76   9.248%   $269.5804   $269.58   $269.60   $269.60  
  Purchase #2 $94.84   10.475%   $104.7745   $104.77   $104.75   $104.80  
  Purchase #3 $213.74   8.542%   $231.9977   $232.00   $232.00   $232.00  
  Purchase #4 $174.54   5.535%   $184.2008   $184.20   $184.20   $184.20  
  Purchase #5 $204.50   4.785%   $214.2853   $214.29   $214.30   $214.30  
  Purchase #6 $228.41   12.616%   $257.2262   $257.23   $257.25   $257.20  
  Purchase #7 $171.63   3.639%   $177.8756   $177.88   $177.90   $177.90  
  7 purchase totals = $1,334.42       $1,439.9405   $1,439.95   $1,440.00   $1,440.00