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	$42.39	10.272%	$46.7443	$46.74	$46.75	$46.70
Purchase #2	$79.83	12.211%	$89.578	$89.58	$89.60	$89.60
Purchase #3	$239.70	13.254%	$271.4698	$271.47	$271.45	$271.50
Purchase #4	$77.40	7.483%	$83.1918	$83.19	$83.20	$83.20
Purchase #5	$67.42	5.515%	$71.1382	$71.14	$71.15	$71.10
Purchase #6	$120.98	11.453%	$134.8358	$134.84	$134.85	$134.80
Purchase #7	$133.71	13.531%	$151.8023	$151.80	$151.80	$151.80
7 purchase totals =	$761.43		$848.7602	$848.76	$848.80	$848.70