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 $223.28   4.711%   $233.7987   $233.80   $233.80   $233.80  
  Purchase #2 $143.66   3.661%   $148.9194   $148.92   $148.90   $148.90  
  Purchase #3 $190.73   5.345%   $200.9245   $200.92   $200.90   $200.90  
  Purchase #4 $115.35   8.125%   $124.7222   $124.72   $124.70   $124.70  
  Purchase #5 $56.39   13.350%   $63.9181   $63.92   $63.90   $63.90  
  Purchase #6 $228.97   3.242%   $236.3932   $236.39   $236.40   $236.40  
  Purchase #7 $9.39   13.295%   $10.6384   $10.64   $10.65   $10.60  
  7 purchase totals = $967.77       $1,019.3145   $1,019.31   $1,019.25   $1,019.20