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 $247.83   6.752%   $264.5635   $264.56   $264.55   $264.60  
  Purchase #2 $33.25   4.871%   $34.8696   $34.87   $34.85   $34.90  
  Purchase #3 $145.84   7.116%   $156.218   $156.22   $156.20   $156.20  
  Purchase #4 $178.37   3.269%   $184.2009   $184.20   $184.20   $184.20  
  Purchase #5 $240.48   11.681%   $268.5705   $268.57   $268.55   $268.60  
  Purchase #6 $27.61   4.837%   $28.9455   $28.95   $28.95   $28.90  
  Purchase #7 $222.69   6.116%   $236.3097   $236.31   $236.30   $236.30  
  7 purchase totals = $1,096.07       $1,173.6777   $1,173.68   $1,173.60   $1,173.70