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	$81.30	9.510%	$89.0316	$89.03	$89.05	$89.00
Purchase #2	$178.63	10.112%	$196.6931	$196.69	$196.70	$196.70
Purchase #3	$168.62	5.401%	$177.7272	$177.73	$177.75	$177.70
Purchase #4	$127.74	9.388%	$139.7322	$139.73	$139.75	$139.70
Purchase #5	$188.50	13.722%	$214.366	$214.37	$214.35	$214.40
Purchase #6	$188.86	11.710%	$210.9755	$210.98	$211.00	$211.00
Purchase #7	$111.99	10.463%	$123.7075	$123.71	$123.70	$123.70
7 purchase totals =	$1,045.64		$1,152.2331	$1,152.24	$1,152.30	$1,152.20