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	$29.95	8.636%	$32.5365	$32.54	$32.55	$32.50
Purchase #2	$60.45	7.703%	$65.1065	$65.11	$65.10	$65.10
Purchase #3	$95.88	4.263%	$99.9674	$99.97	$99.95	$100.00
Purchase #4	$112.93	9.362%	$123.5025	$123.50	$123.50	$123.50
Purchase #5	$163.73	6.312%	$174.0646	$174.06	$174.05	$174.10
Purchase #6	$204.43	3.784%	$212.1656	$212.17	$212.15	$212.20
Purchase #7	$36.45	12.280%	$40.9261	$40.93	$40.95	$40.90
7 purchase totals =	$703.82		$748.2692	$748.28	$748.25	$748.30