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 $241.84   10.255%   $266.6407   $266.64   $266.65   $266.60  
  Purchase #2 $60.32   5.569%   $63.6792   $63.68   $63.70   $63.70  
  Purchase #3 $206.89   5.189%   $217.6255   $217.63   $217.65   $217.60  
  Purchase #4 $84.30   11.827%   $94.2702   $94.27   $94.25   $94.30  
  Purchase #5 $207.82   11.729%   $232.1952   $232.20   $232.20   $232.20  
  Purchase #6 $74.33   7.273%   $79.736   $79.74   $79.75   $79.70  
  Purchase #7 $106.74   6.598%   $113.7827   $113.78   $113.80   $113.80  
  7 purchase totals = $982.24       $1,067.9295   $1,067.94   $1,068.00   $1,067.90