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 $119.61   9.273%   $130.7014   $130.70   $130.70   $130.70  
  Purchase #2 $184.90   11.534%   $206.2264   $206.23   $206.25   $206.20  
  Purchase #3 $76.42   13.705%   $86.8934   $86.89   $86.90   $86.90  
  Purchase #4 $221.73   5.427%   $233.7633   $233.76   $233.75   $233.80  
  Purchase #5 $240.73   13.244%   $272.6123   $272.61   $272.60   $272.60  
  Purchase #6 $207.97   8.801%   $226.2734   $226.27   $226.25   $226.30  
  Purchase #7 $67.61   8.657%   $73.463   $73.46   $73.45   $73.50  
  7 purchase totals = $1,118.97       $1,229.9332   $1,229.92   $1,229.90   $1,230.00