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 $82.28   4.867%   $86.2846   $86.28   $86.30   $86.30  
  Purchase #2 $16.94   9.782%   $18.5971   $18.60   $18.60   $18.60  
  Purchase #3 $109.93   5.743%   $116.2433   $116.24   $116.25   $116.20  
  Purchase #4 $50.46   13.395%   $57.2191   $57.22   $57.20   $57.20  
  Purchase #5 $24.43   7.831%   $26.3431   $26.34   $26.35   $26.30  
  Purchase #6 $190.70   9.190%   $208.2253   $208.23   $208.25   $208.20  
  Purchase #7 $235.55   4.458%   $246.0508   $246.05   $246.05   $246.10  
  7 purchase totals = $710.29       $758.9633   $758.96   $759.00   $758.90