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	$236.88	8.139%	$256.1597	$256.16	$256.15	$256.20
Purchase #2	$54.78	8.314%	$59.3344	$59.33	$59.35	$59.30
Purchase #3	$70.43	6.247%	$74.8298	$74.83	$74.85	$74.80
Purchase #4	$187.71	10.425%	$207.2788	$207.28	$207.30	$207.30
Purchase #5	$162.74	13.313%	$184.4056	$184.41	$184.40	$184.40
Purchase #6	$123.44	13.279%	$139.8316	$139.83	$139.85	$139.80
Purchase #7	$75.94	8.519%	$82.4093	$82.41	$82.40	$82.40
7 purchase totals =	$911.92		$1,004.2492	$1,004.25	$1,004.30	$1,004.20