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	$81.38	11.528%	$90.7615	$90.76	$90.75	$90.80
Purchase #2	$129.95	13.530%	$147.5322	$147.53	$147.55	$147.50
Purchase #3	$143.73	3.392%	$148.6053	$148.61	$148.60	$148.60
Purchase #4	$121.32	12.151%	$136.0616	$136.06	$136.05	$136.10
Purchase #5	$11.96	10.851%	$13.2578	$13.26	$13.25	$13.30
Purchase #6	$190.82	10.370%	$210.608	$210.61	$210.60	$210.60
Purchase #7	$103.72	5.846%	$109.7835	$109.78	$109.80	$109.80
7 purchase totals =	$782.88		$856.6099	$856.61	$856.60	$856.70