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 $206.99   8.797%   $225.1989   $225.20   $225.20   $225.20  
  Purchase #2 $163.96   12.343%   $184.1976   $184.20   $184.20   $184.20  
  Purchase #3 $129.58   10.637%   $143.3634   $143.36   $143.35   $143.40  
  Purchase #4 $144.56   6.177%   $153.4895   $153.49   $153.50   $153.50  
  Purchase #5 $148.94   11.606%   $166.226   $166.23   $166.25   $166.20  
  Purchase #6 $250.82   6.390%   $266.8474   $266.85   $266.85   $266.80  
  Purchase #7 $130.74   13.695%   $148.6448   $148.64   $148.65   $148.60  
  7 purchase totals = $1,175.59       $1,287.9676   $1,287.97   $1,288.00   $1,287.90