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	$64.90	13.829%	$73.875	$73.88	$73.90	$73.90
Purchase #2	$205.96	11.317%	$229.2685	$229.27	$229.25	$229.30
Purchase #3	$48.68	5.843%	$51.5244	$51.52	$51.50	$51.50
Purchase #4	$89.27	8.770%	$97.099	$97.10	$97.10	$97.10
Purchase #5	$115.96	10.303%	$127.9074	$127.91	$127.90	$127.90
Purchase #6	$59.60	13.641%	$67.73	$67.73	$67.75	$67.70
Purchase #7	$157.82	11.845%	$176.5138	$176.51	$176.50	$176.50
7 purchase totals =	$742.19		$823.9181	$823.92	$823.90	$823.90