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 $63.76   10.159%   $70.2374   $70.24   $70.25   $70.20  
  Purchase #2 $77.44   11.865%   $86.6283   $86.63   $86.65   $86.60  
  Purchase #3 $140.87   8.756%   $153.2046   $153.20   $153.20   $153.20  
  Purchase #4 $23.93   10.434%   $26.4269   $26.43   $26.45   $26.40  
  Purchase #5 $189.81   4.839%   $198.9949   $198.99   $199.00   $199.00  
  Purchase #6 $188.65   13.445%   $214.014   $214.01   $214.00   $214.00  
  Purchase #7 $11.75   5.401%   $12.3846   $12.38   $12.40   $12.40  
  7 purchase totals = $696.21       $761.8907   $761.88   $761.95   $761.80