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	$89.87	10.561%	$99.3612	$99.36	$99.35	$99.40
Purchase #2	$45.35	9.726%	$49.7607	$49.76	$49.75	$49.80
Purchase #3	$244.93	13.798%	$278.7254	$278.73	$278.75	$278.70
Purchase #4	$139.49	3.688%	$144.6344	$144.63	$144.65	$144.60
Purchase #5	$54.92	11.754%	$61.3753	$61.38	$61.40	$61.40
Purchase #6	$72.93	6.757%	$77.8579	$77.86	$77.85	$77.90
Purchase #7	$76.76	13.244%	$86.9261	$86.93	$86.95	$86.90
7 purchase totals =	$724.25		$798.6410	$798.65	$798.70	$798.70