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 $246.93   6.169%   $262.1631   $262.16   $262.15   $262.20  
  Purchase #2 $96.84   8.361%   $104.9368   $104.94   $104.95   $104.90  
  Purchase #3 $192.71   12.678%   $217.1418   $217.14   $217.15   $217.10  
  Purchase #4 $47.38   5.678%   $50.0702   $50.07   $50.05   $50.10  
  Purchase #5 $184.27   8.300%   $199.5644   $199.56   $199.55   $199.60  
  Purchase #6 $81.49   3.642%   $84.4579   $84.46   $84.45   $84.50  
  Purchase #7 $189.38   5.773%   $200.3129   $200.31   $200.30   $200.30  
  7 purchase totals = $1,039.00       $1,118.6471   $1,118.64   $1,118.60   $1,118.70