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 $62.76   10.426%   $69.3034   $69.30   $69.30   $69.30  
  Purchase #2 $91.93   12.272%   $103.2116   $103.21   $103.20   $103.20  
  Purchase #3 $133.85   11.176%   $148.8091   $148.81   $148.80   $148.80  
  Purchase #4 $62.80   3.851%   $65.2184   $65.22   $65.20   $65.20  
  Purchase #5 $236.46   4.347%   $246.7389   $246.74   $246.75   $246.70  
  Purchase #6 $55.47   3.807%   $57.5817   $57.58   $57.60   $57.60  
  Purchase #7 $98.33   5.665%   $103.9004   $103.90   $103.90   $103.90  
  7 purchase totals = $741.60       $794.7635   $794.76   $794.75   $794.70