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	$103.27	3.783%	$107.1767	$107.18	$107.20	$107.20
Purchase #2	$170.29	10.863%	$188.7886	$188.79	$188.80	$188.80
Purchase #3	$194.73	3.167%	$200.8971	$200.90	$200.90	$200.90
Purchase #4	$217.76	4.191%	$226.8863	$226.89	$226.90	$226.90
Purchase #5	$37.85	10.469%	$41.8125	$41.81	$41.80	$41.80
Purchase #6	$49.54	8.628%	$53.8143	$53.81	$53.80	$53.80
Purchase #7	$233.75	13.295%	$264.8271	$264.83	$264.85	$264.80
7 purchase totals =	$1,007.19		$1,084.2026	$1,084.21	$1,084.25	$1,084.20