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 $232.59   8.871%   $253.2231   $253.22   $253.20   $253.20  
  Purchase #2 $116.28   5.545%   $122.7277   $122.73   $122.75   $122.70  
  Purchase #3 $153.63   11.459%   $171.2345   $171.23   $171.25   $171.20  
  Purchase #4 $214.75   6.211%   $228.0881   $228.09   $228.10   $228.10  
  Purchase #5 $162.25   8.180%   $175.5221   $175.52   $175.50   $175.50  
  Purchase #6 $240.85   4.151%   $250.8477   $250.85   $250.85   $250.80  
  Purchase #7 $10.37   9.462%   $11.3512   $11.35   $11.35   $11.40  
  7 purchase totals = $1,130.72       $1,212.9944   $1,212.99   $1,213.00   $1,212.90