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	$238.47	12.765%	$268.9107	$268.91	$268.90	$268.90
Purchase #2	$21.64	10.418%	$23.8945	$23.89	$23.90	$23.90
Purchase #3	$206.42	4.705%	$216.1321	$216.13	$216.15	$216.10
Purchase #4	$219.83	11.123%	$244.2817	$244.28	$244.30	$244.30
Purchase #5	$38.37	7.228%	$41.1434	$41.14	$41.15	$41.10
Purchase #6	$145.38	9.140%	$158.6677	$158.67	$158.65	$158.70
Purchase #7	$49.33	3.578%	$51.095	$51.10	$51.10	$51.10
7 purchase totals =	$919.44		$1,004.1251	$1,004.12	$1,004.15	$1,004.10