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 $221.31   9.325%   $241.9472   $241.95   $241.95   $241.90  
  Purchase #2 $41.57   8.872%   $45.2581   $45.26   $45.25   $45.30  
  Purchase #3 $27.75   10.643%   $30.7034   $30.70   $30.70   $30.70  
  Purchase #4 $248.85   3.740%   $258.157   $258.16   $258.15   $258.20  
  Purchase #5 $95.51   8.235%   $103.3752   $103.38   $103.40   $103.40  
  Purchase #6 $31.90   8.418%   $34.5853   $34.59   $34.60   $34.60  
  Purchase #7 $136.58   8.761%   $148.5458   $148.55   $148.55   $148.50  
  7 purchase totals = $803.47       $862.5720   $862.59   $862.60   $862.60