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	$50.75	11.428%	$56.5497	$56.55	$56.55	$56.50
Purchase #2	$92.36	10.371%	$101.9387	$101.94	$101.95	$101.90
Purchase #3	$33.89	10.361%	$37.4013	$37.40	$37.40	$37.40
Purchase #4	$153.32	3.611%	$158.8564	$158.86	$158.85	$158.90
Purchase #5	$63.49	10.587%	$70.2117	$70.21	$70.20	$70.20
Purchase #6	$126.78	11.758%	$141.6868	$141.69	$141.70	$141.70
Purchase #7	$74.77	6.304%	$79.4835	$79.48	$79.50	$79.50
7 purchase totals =	$595.36		$646.1281	$646.13	$646.15	$646.10