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	$42.88	6.820%	$45.8044	$45.80	$45.80	$45.80
Purchase #2	$246.57	3.537%	$255.2912	$255.29	$255.30	$255.30
Purchase #3	$87.54	3.502%	$90.6057	$90.61	$90.60	$90.60
Purchase #4	$138.58	11.325%	$154.2742	$154.27	$154.25	$154.30
Purchase #5	$149.73	10.750%	$165.826	$165.83	$165.85	$165.80
Purchase #6	$94.76	7.454%	$101.8234	$101.82	$101.80	$101.80
Purchase #7	$5.35	7.553%	$5.7541	$5.75	$5.75	$5.80
7 purchase totals =	$765.41		$819.3790	$819.37	$819.35	$819.40