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	$18.44	6.535%	$19.6451	$19.65	$19.65	$19.60
Purchase #2	$96.44	4.534%	$100.8126	$100.81	$100.80	$100.80
Purchase #3	$137.45	4.210%	$143.2366	$143.24	$143.25	$143.20
Purchase #4	$223.40	10.632%	$247.1519	$247.15	$247.15	$247.20
Purchase #5	$30.55	9.379%	$33.4153	$33.42	$33.40	$33.40
Purchase #6	$219.45	7.226%	$235.3075	$235.31	$235.30	$235.30
Purchase #7	$82.42	9.331%	$90.1106	$90.11	$90.10	$90.10
7 purchase totals =	$808.15		$869.6796	$869.69	$869.65	$869.60