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	$65.83	8.418%	$71.3716	$71.37	$71.35	$71.40
Purchase #2	$182.95	6.376%	$194.6149	$194.61	$194.60	$194.60
Purchase #3	$205.47	11.859%	$229.8367	$229.84	$229.85	$229.80
Purchase #4	$189.69	10.192%	$209.0232	$209.02	$209.00	$209.00
Purchase #5	$188.84	6.111%	$200.38	$200.38	$200.40	$200.40
Purchase #6	$33.95	12.752%	$38.2793	$38.28	$38.30	$38.30
Purchase #7	$36.78	4.379%	$38.3906	$38.39	$38.40	$38.40
7 purchase totals =	$903.51		$981.8963	$981.89	$981.90	$981.90