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 $232.49   5.826%   $246.0349   $246.03   $246.05   $246.00  
  Purchase #2 $200.96   12.702%   $226.4859   $226.49   $226.50   $226.50  
  Purchase #3 $94.81   13.849%   $107.9402   $107.94   $107.95   $107.90  
  Purchase #4 $219.85   13.756%   $250.0926   $250.09   $250.10   $250.10  
  Purchase #5 $81.36   4.362%   $84.9089   $84.91   $84.90   $84.90  
  Purchase #6 $238.76   11.165%   $265.4176   $265.42   $265.40   $265.40  
  Purchase #7 $188.74   13.688%   $214.5747   $214.57   $214.55   $214.60  
  7 purchase totals = $1,256.97       $1,395.4548   $1,395.45   $1,395.45   $1,395.40