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	$90.83	10.731%	$100.577	$100.58	$100.60	$100.60
Purchase #2	$127.47	12.860%	$143.8626	$143.86	$143.85	$143.90
Purchase #3	$19.75	12.488%	$22.2164	$22.22	$22.20	$22.20
Purchase #4	$239.63	8.178%	$259.2269	$259.23	$259.25	$259.20
Purchase #5	$243.54	9.437%	$266.5229	$266.52	$266.50	$266.50
Purchase #6	$80.32	7.871%	$86.642	$86.64	$86.65	$86.60
Purchase #7	$250.59	7.695%	$269.8729	$269.87	$269.85	$269.90
7 purchase totals =	$1,052.13		$1,148.9207	$1,148.92	$1,148.90	$1,148.90