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	$31.58	6.180%	$33.5316	$33.53	$33.55	$33.50
Purchase #2	$124.88	11.536%	$139.2862	$139.29	$139.30	$139.30
Purchase #3	$193.83	5.581%	$204.6477	$204.65	$204.65	$204.60
Purchase #4	$178.56	11.333%	$198.7962	$198.80	$198.80	$198.80
Purchase #5	$84.78	5.578%	$89.509	$89.51	$89.50	$89.50
Purchase #6	$109.31	12.569%	$123.0492	$123.05	$123.05	$123.00
Purchase #7	$115.71	10.609%	$127.9857	$127.99	$128.00	$128.00
7 purchase totals =	$838.65		$916.8056	$916.82	$916.85	$916.70