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	$159.59	7.145%	$170.9927	$170.99	$171.00	$171.00
Purchase #2	$105.98	3.404%	$109.5876	$109.59	$109.60	$109.60
Purchase #3	$103.78	12.613%	$116.8698	$116.87	$116.85	$116.90
Purchase #4	$54.93	7.236%	$58.9047	$58.90	$58.90	$58.90
Purchase #5	$176.29	3.717%	$182.8427	$182.84	$182.85	$182.80
Purchase #6	$82.84	7.251%	$88.8467	$88.85	$88.85	$88.80
Purchase #7	$247.98	10.517%	$274.0601	$274.06	$274.05	$274.10
7 purchase totals =	$931.39		$1,002.1043	$1,002.10	$1,002.10	$1,002.10