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	$49.71	11.542%	$55.4475	$55.45	$55.45	$55.40
Purchase #2	$173.72	8.705%	$188.8423	$188.84	$188.85	$188.80
Purchase #3	$58.92	4.597%	$61.6286	$61.63	$61.65	$61.60
Purchase #4	$241.65	8.222%	$261.5185	$261.52	$261.50	$261.50
Purchase #5	$28.84	12.627%	$32.4816	$32.48	$32.50	$32.50
Purchase #6	$18.85	3.358%	$19.483	$19.48	$19.50	$19.50
Purchase #7	$26.71	5.292%	$28.1235	$28.12	$28.10	$28.10
7 purchase totals =	$598.40		$647.5250	$647.52	$647.55	$647.40