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	$83.34	7.754%	$89.8022	$89.80	$89.80	$89.80
Purchase #2	$24.85	9.290%	$27.1586	$27.16	$27.15	$27.20
Purchase #3	$145.36	4.834%	$152.3867	$152.39	$152.40	$152.40
Purchase #4	$111.94	10.625%	$123.8336	$123.83	$123.85	$123.80
Purchase #5	$91.70	7.584%	$98.6545	$98.65	$98.65	$98.70
Purchase #6	$54.56	10.212%	$60.1317	$60.13	$60.15	$60.10
Purchase #7	$75.62	6.787%	$80.7523	$80.75	$80.75	$80.80
7 purchase totals =	$587.37		$632.7196	$632.71	$632.75	$632.80