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	$110.66	5.300%	$116.525	$116.53	$116.55	$116.50
Purchase #2	$83.39	7.660%	$89.7777	$89.78	$89.80	$89.80
Purchase #3	$86.74	3.107%	$89.435	$89.44	$89.45	$89.40
Purchase #4	$97.64	4.277%	$101.8161	$101.82	$101.80	$101.80
Purchase #5	$175.88	6.114%	$186.6333	$186.63	$186.65	$186.60
Purchase #6	$190.44	11.104%	$211.5865	$211.59	$211.60	$211.60
Purchase #7	$25.72	13.510%	$29.1948	$29.19	$29.20	$29.20
7 purchase totals =	$770.47		$824.9684	$824.98	$825.05	$824.90