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 $246.77   10.692%   $273.1546   $273.15   $273.15   $273.20  
  Purchase #2 $188.58   6.239%   $200.3455   $200.35   $200.35   $200.30  
  Purchase #3 $201.55   6.105%   $213.8546   $213.85   $213.85   $213.90  
  Purchase #4 $164.40   10.258%   $181.2642   $181.26   $181.25   $181.30  
  Purchase #5 $143.74   6.489%   $153.0673   $153.07   $153.05   $153.10  
  Purchase #6 $12.63   6.126%   $13.4037   $13.40   $13.40   $13.40  
  Purchase #7 $106.39   8.862%   $115.8183   $115.82   $115.80   $115.80  
  7 purchase totals = $1,064.06       $1,150.9082   $1,150.90   $1,150.85   $1,151.00