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 $60.53   4.612%   $63.3216   $63.32   $63.30   $63.30  
  Purchase #2 $222.97   13.855%   $253.8625   $253.86   $253.85   $253.90  
  Purchase #3 $157.32   8.459%   $170.6277   $170.63   $170.65   $170.60  
  Purchase #4 $124.54   10.412%   $137.5071   $137.51   $137.50   $137.50  
  Purchase #5 $10.59   7.142%   $11.3463   $11.35   $11.35   $11.30  
  Purchase #6 $15.98   10.543%   $17.6648   $17.66   $17.65   $17.70  
  Purchase #7 $90.40   3.514%   $93.5767   $93.58   $93.60   $93.60  
  7 purchase totals = $682.33       $747.9067   $747.91   $747.90   $747.90