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	$99.94	11.264%	$111.1972	$111.20	$111.20	$111.20
Purchase #2	$193.30	3.784%	$200.6145	$200.61	$200.60	$200.60
Purchase #3	$139.28	3.347%	$143.9417	$143.94	$143.95	$143.90
Purchase #4	$245.88	3.607%	$254.7489	$254.75	$254.75	$254.70
Purchase #5	$112.75	4.296%	$117.5937	$117.59	$117.60	$117.60
Purchase #6	$39.75	11.585%	$44.355	$44.36	$44.35	$44.40
Purchase #7	$124.58	13.408%	$141.2837	$141.28	$141.30	$141.30
7 purchase totals =	$955.48		$1,013.7347	$1,013.73	$1,013.75	$1,013.70