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 $60.59   9.359%   $66.2606   $66.26   $66.25   $66.30  
  Purchase #2 $143.46   7.130%   $153.6887   $153.69   $153.70   $153.70  
  Purchase #3 $144.46   7.490%   $155.2801   $155.28   $155.30   $155.30  
  Purchase #4 $101.64   4.316%   $106.0268   $106.03   $106.05   $106.00  
  Purchase #5 $81.43   6.118%   $86.4119   $86.41   $86.40   $86.40  
  Purchase #6 $121.86   12.352%   $136.9121   $136.91   $136.90   $136.90  
  Purchase #7 $73.86   5.748%   $78.1055   $78.11   $78.10   $78.10  
  7 purchase totals = $727.30       $782.6857   $782.69   $782.70   $782.70