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 $10.58   6.172%   $11.233   $11.23   $11.25   $11.20  
  Purchase #2 $50.90   5.313%   $53.6043   $53.60   $53.60   $53.60  
  Purchase #3 $8.54   8.307%   $9.2494   $9.25   $9.25   $9.20  
  Purchase #4 $71.79   6.521%   $76.4714   $76.47   $76.45   $76.50  
  Purchase #5 $84.33   13.418%   $95.6454   $95.65   $95.65   $95.60  
  Purchase #6 $8.93   4.724%   $9.3519   $9.35   $9.35   $9.40  
  Purchase #7 $139.33   8.401%   $151.0351   $151.04   $151.05   $151.00  
  7 purchase totals = $374.40       $406.5905   $406.59   $406.60   $406.50