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	$37.92	13.281%	$42.9562	$42.96	$42.95	$43.00
Purchase #2	$144.72	7.626%	$155.7563	$155.76	$155.75	$155.80
Purchase #3	$16.93	5.304%	$17.828	$17.83	$17.85	$17.80
Purchase #4	$51.69	6.679%	$55.1424	$55.14	$55.15	$55.10
Purchase #5	$32.98	13.330%	$37.3762	$37.38	$37.40	$37.40
Purchase #6	$57.86	4.454%	$60.4371	$60.44	$60.45	$60.40
Purchase #7	$200.85	6.461%	$213.8269	$213.83	$213.85	$213.80
7 purchase totals =	$542.95		$583.3231	$583.34	$583.40	$583.30