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	$81.53	4.722%	$85.3798	$85.38	$85.40	$85.40
Purchase #2	$83.95	6.123%	$89.0903	$89.09	$89.10	$89.10
Purchase #3	$222.42	5.546%	$234.7554	$234.76	$234.75	$234.80
Purchase #4	$124.38	10.193%	$137.0581	$137.06	$137.05	$137.10
Purchase #5	$36.74	3.429%	$37.9998	$38.00	$38.00	$38.00
Purchase #6	$178.89	6.874%	$191.1869	$191.19	$191.20	$191.20
Purchase #7	$151.90	9.729%	$166.6784	$166.68	$166.70	$166.70
7 purchase totals =	$879.81		$942.1487	$942.16	$942.20	$942.30