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	$155.34	9.749%	$170.4841	$170.48	$170.50	$170.50
Purchase #2	$28.34	3.191%	$29.2443	$29.24	$29.25	$29.20
Purchase #3	$19.40	5.783%	$20.5219	$20.52	$20.50	$20.50
Purchase #4	$134.31	9.632%	$147.2467	$147.25	$147.25	$147.20
Purchase #5	$115.43	13.832%	$131.3963	$131.40	$131.40	$131.40
Purchase #6	$151.30	13.178%	$171.2383	$171.24	$171.25	$171.20
Purchase #7	$56.49	13.804%	$64.2879	$64.29	$64.30	$64.30
7 purchase totals =	$660.61		$734.4195	$734.42	$734.45	$734.30