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	$86.28	9.303%	$94.3066	$94.31	$94.30	$94.30
Purchase #2	$190.42	4.814%	$199.5868	$199.59	$199.60	$199.60
Purchase #3	$31.60	4.856%	$33.1345	$33.13	$33.15	$33.10
Purchase #4	$89.31	6.300%	$94.9365	$94.94	$94.95	$94.90
Purchase #5	$239.63	11.197%	$266.4614	$266.46	$266.45	$266.50
Purchase #6	$57.54	8.552%	$62.4608	$62.46	$62.45	$62.50
Purchase #7	$72.69	13.104%	$82.2153	$82.22	$82.20	$82.20
7 purchase totals =	$767.47		$833.1019	$833.11	$833.10	$833.10