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 $240.69   9.761%   $264.1838   $264.18   $264.20   $264.20  
  Purchase #2 $103.55   11.588%   $115.5494   $115.55   $115.55   $115.50  
  Purchase #3 $242.59   9.554%   $265.767   $265.77   $265.75   $265.80  
  Purchase #4 $54.53   7.724%   $58.7419   $58.74   $58.75   $58.70  
  Purchase #5 $182.63   11.754%   $204.0963   $204.10   $204.10   $204.10  
  Purchase #6 $143.66   6.647%   $153.2091   $153.21   $153.20   $153.20  
  Purchase #7 $173.61   10.794%   $192.3495   $192.35   $192.35   $192.30  
  7 purchase totals = $1,141.26       $1,253.8970   $1,253.90   $1,253.90   $1,253.80