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 $32.63   6.242%   $34.6668   $34.67   $34.65   $34.70  
  Purchase #2 $224.64   7.417%   $241.3015   $241.30   $241.30   $241.30  
  Purchase #3 $96.50   3.197%   $99.5851   $99.59   $99.60   $99.60  
  Purchase #4 $183.94   5.215%   $193.5325   $193.53   $193.55   $193.50  
  Purchase #5 $34.47   10.326%   $38.0294   $38.03   $38.05   $38.00  
  Purchase #6 $231.99   8.261%   $251.1547   $251.15   $251.15   $251.20  
  Purchase #7 $137.39   6.527%   $146.3574   $146.36   $146.35   $146.40  
  7 purchase totals = $941.56       $1,004.6274   $1,004.63   $1,004.65   $1,004.70