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	$137.74	6.671%	$146.9286	$146.93	$146.95	$146.90
Purchase #2	$61.96	8.865%	$67.4528	$67.45	$67.45	$67.50
Purchase #3	$225.75	4.841%	$236.6786	$236.68	$236.70	$236.70
Purchase #4	$48.76	7.825%	$52.5755	$52.58	$52.60	$52.60
Purchase #5	$213.44	4.195%	$222.3938	$222.39	$222.40	$222.40
Purchase #6	$189.79	10.733%	$210.1602	$210.16	$210.15	$210.20
Purchase #7	$43.31	4.646%	$45.3222	$45.32	$45.30	$45.30
7 purchase totals =	$920.75		$981.5117	$981.51	$981.55	$981.60