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 $248.60   10.290%   $274.1809   $274.18   $274.20   $274.20  
  Purchase #2 $24.26   5.743%   $25.6533   $25.65   $25.65   $25.70  
  Purchase #3 $218.83   10.128%   $240.9931   $240.99   $241.00   $241.00  
  Purchase #4 $169.33   3.679%   $175.5597   $175.56   $175.55   $175.60  
  Purchase #5 $178.77   7.401%   $192.0008   $192.00   $192.00   $192.00  
  Purchase #6 $88.45   8.190%   $95.6941   $95.69   $95.70   $95.70  
  Purchase #7 $30.92   8.591%   $33.5763   $33.58   $33.60   $33.60  
  7 purchase totals = $959.16       $1,037.6582   $1,037.65   $1,037.70   $1,037.80