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	$88.92	13.336%	$100.7784	$100.78	$100.80	$100.80
Purchase #2	$143.48	3.358%	$148.2981	$148.30	$148.30	$148.30
Purchase #3	$200.71	9.477%	$219.7313	$219.73	$219.75	$219.70
Purchase #4	$113.44	12.792%	$127.9512	$127.95	$127.95	$128.00
Purchase #5	$196.27	12.814%	$221.42	$221.42	$221.40	$221.40
Purchase #6	$210.89	8.721%	$229.2817	$229.28	$229.30	$229.30
Purchase #7	$96.58	9.404%	$105.6624	$105.66	$105.65	$105.70
7 purchase totals =	$1,050.29		$1,153.1231	$1,153.12	$1,153.15	$1,153.20