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 $89.36   10.402%   $98.6552   $98.66   $98.65   $98.70  
  Purchase #2 $185.61   7.708%   $199.9168   $199.92   $199.90   $199.90  
  Purchase #3 $214.78   8.439%   $232.9053   $232.91   $232.90   $232.90  
  Purchase #4 $55.30   9.570%   $60.5922   $60.59   $60.60   $60.60  
  Purchase #5 $169.77   13.324%   $192.3902   $192.39   $192.40   $192.40  
  Purchase #6 $23.46   5.569%   $24.7665   $24.77   $24.75   $24.80  
  Purchase #7 $234.64   7.136%   $251.3839   $251.38   $251.40   $251.40  
  7 purchase totals = $972.92       $1,060.6101   $1,060.62   $1,060.60   $1,060.70