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	$19.38	5.709%	$20.4864	$20.49	$20.50	$20.50
Purchase #2	$238.71	8.772%	$259.6496	$259.65	$259.65	$259.60
Purchase #3	$99.44	12.234%	$111.6055	$111.61	$111.60	$111.60
Purchase #4	$182.41	7.110%	$195.3794	$195.38	$195.40	$195.40
Purchase #5	$60.61	10.269%	$66.834	$66.83	$66.85	$66.80
Purchase #6	$226.77	9.749%	$248.8778	$248.88	$248.90	$248.90
Purchase #7	$146.53	5.361%	$154.3855	$154.39	$154.40	$154.40
7 purchase totals =	$973.85		$1,057.2182	$1,057.23	$1,057.30	$1,057.20