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	$95.91	4.674%	$100.3928	$100.39	$100.40	$100.40
Purchase #2	$157.26	5.707%	$166.2348	$166.23	$166.25	$166.20
Purchase #3	$121.40	6.152%	$128.8685	$128.87	$128.85	$128.90
Purchase #4	$80.79	9.452%	$88.4263	$88.43	$88.45	$88.40
Purchase #5	$188.39	5.538%	$198.823	$198.82	$198.80	$198.80
Purchase #6	$56.68	4.370%	$59.1569	$59.16	$59.15	$59.20
Purchase #7	$155.32	6.141%	$164.8582	$164.86	$164.85	$164.90
7 purchase totals =	$855.75		$906.7605	$906.76	$906.75	$906.80