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	$42.64	6.746%	$45.5165	$45.52	$45.50	$45.50
Purchase #2	$46.51	5.128%	$48.895	$48.90	$48.90	$48.90
Purchase #3	$9.97	7.753%	$10.743	$10.74	$10.75	$10.70
Purchase #4	$33.79	13.502%	$38.3523	$38.35	$38.35	$38.40
Purchase #5	$176.37	13.641%	$200.4286	$200.43	$200.45	$200.40
Purchase #6	$87.65	12.678%	$98.7623	$98.76	$98.75	$98.80
Purchase #7	$165.32	6.780%	$176.5287	$176.53	$176.55	$176.50
7 purchase totals =	$562.25		$619.2264	$619.23	$619.25	$619.20