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	$210.54	8.566%	$228.5749	$228.57	$228.55	$228.60
Purchase #2	$168.66	3.335%	$174.2848	$174.28	$174.30	$174.30
Purchase #3	$248.45	12.467%	$279.4243	$279.42	$279.40	$279.40
Purchase #4	$43.43	12.191%	$48.7246	$48.72	$48.70	$48.70
Purchase #5	$45.53	9.340%	$49.7825	$49.78	$49.80	$49.80
Purchase #6	$247.82	9.301%	$270.8697	$270.87	$270.85	$270.90
Purchase #7	$89.92	12.480%	$101.142	$101.14	$101.15	$101.10
7 purchase totals =	$1,054.35		$1,152.8028	$1,152.78	$1,152.75	$1,152.80