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	$52.90	3.576%	$54.7917	$54.79	$54.80	$54.80
Purchase #2	$234.55	10.240%	$258.5679	$258.57	$258.55	$258.60
Purchase #3	$185.72	4.513%	$194.1015	$194.10	$194.10	$194.10
Purchase #4	$207.76	10.118%	$228.7812	$228.78	$228.80	$228.80
Purchase #5	$16.68	10.765%	$18.4756	$18.48	$18.50	$18.50
Purchase #6	$90.47	11.487%	$100.8623	$100.86	$100.85	$100.90
Purchase #7	$201.32	7.156%	$215.7265	$215.73	$215.75	$215.70
7 purchase totals =	$989.40		$1,071.3067	$1,071.31	$1,071.35	$1,071.40