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 $68.91   10.414%   $76.0863   $76.09   $76.10   $76.10  
  Purchase #2 $41.37   5.562%   $43.671   $43.67   $43.65   $43.70  
  Purchase #3 $78.81   9.152%   $86.0227   $86.02   $86.00   $86.00  
  Purchase #4 $236.32   8.695%   $256.868   $256.87   $256.85   $256.90  
  Purchase #5 $122.75   6.300%   $130.4833   $130.48   $130.50   $130.50  
  Purchase #6 $18.51   3.416%   $19.1423   $19.14   $19.15   $19.10  
  Purchase #7 $240.31   4.345%   $250.7515   $250.75   $250.75   $250.80  
  7 purchase totals = $806.98       $863.0251   $863.02   $863.00   $863.10