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	$69.49	3.729%	$72.0813	$72.08	$72.10	$72.10
Purchase #2	$83.36	7.745%	$89.8162	$89.82	$89.80	$89.80
Purchase #3	$55.36	5.788%	$58.5642	$58.56	$58.55	$58.60
Purchase #4	$15.89	12.370%	$17.8556	$17.86	$17.85	$17.90
Purchase #5	$109.78	4.135%	$114.3194	$114.32	$114.30	$114.30
Purchase #6	$100.91	4.194%	$105.1422	$105.14	$105.15	$105.10
Purchase #7	$102.58	3.274%	$105.9385	$105.94	$105.95	$105.90
7 purchase totals =	$537.37		$563.7174	$563.72	$563.70	$563.70