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	$157.91	4.815%	$165.5134	$165.51	$165.50	$165.50
Purchase #2	$36.69	9.105%	$40.0306	$40.03	$40.05	$40.00
Purchase #3	$80.93	8.835%	$88.0802	$88.08	$88.10	$88.10
Purchase #4	$40.55	3.714%	$42.056	$42.06	$42.05	$42.10
Purchase #5	$149.27	6.816%	$159.4442	$159.44	$159.45	$159.40
Purchase #6	$68.78	5.399%	$72.4934	$72.49	$72.50	$72.50
Purchase #7	$27.64	6.253%	$29.3683	$29.37	$29.35	$29.40
7 purchase totals =	$561.77		$596.9861	$596.98	$597.00	$597.00