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	$54.64	13.313%	$61.9142	$61.91	$61.90	$61.90
Purchase #2	$48.97	13.227%	$55.4473	$55.45	$55.45	$55.40
Purchase #3	$89.71	11.459%	$99.9899	$99.99	$100.00	$100.00
Purchase #4	$202.31	13.221%	$229.0574	$229.06	$229.05	$229.10
Purchase #5	$54.59	9.295%	$59.6641	$59.66	$59.65	$59.70
Purchase #6	$17.63	11.762%	$19.7036	$19.70	$19.70	$19.70
Purchase #7	$105.64	13.838%	$120.2585	$120.26	$120.25	$120.30
7 purchase totals =	$573.49		$646.0350	$646.03	$646.00	$646.10