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	$146.66	8.363%	$158.9252	$158.93	$158.95	$158.90
Purchase #2	$122.69	7.283%	$131.6255	$131.63	$131.65	$131.60
Purchase #3	$17.86	11.454%	$19.9057	$19.91	$19.90	$19.90
Purchase #4	$63.87	12.623%	$71.9323	$71.93	$71.95	$71.90
Purchase #5	$95.61	4.744%	$100.1457	$100.15	$100.15	$100.10
Purchase #6	$192.54	11.693%	$215.0537	$215.05	$215.05	$215.10
Purchase #7	$100.78	12.217%	$113.0923	$113.09	$113.10	$113.10
7 purchase totals =	$740.01		$810.6804	$810.69	$810.75	$810.60