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	$127.48	8.777%	$138.6689	$138.67	$138.65	$138.70
Purchase #2	$85.89	5.864%	$90.9266	$90.93	$90.95	$90.90
Purchase #3	$162.93	10.202%	$179.5521	$179.55	$179.55	$179.60
Purchase #4	$135.71	3.557%	$140.5372	$140.54	$140.55	$140.50
Purchase #5	$156.26	10.370%	$172.4642	$172.46	$172.45	$172.50
Purchase #6	$111.77	3.819%	$116.0385	$116.04	$116.05	$116.00
Purchase #7	$52.44	7.491%	$56.3683	$56.37	$56.35	$56.40
7 purchase totals =	$832.48		$894.5558	$894.56	$894.55	$894.60