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	$51.77	11.593%	$57.7717	$57.77	$57.75	$57.80
Purchase #2	$43.71	8.730%	$47.5259	$47.53	$47.55	$47.50
Purchase #3	$32.58	11.349%	$36.2775	$36.28	$36.30	$36.30
Purchase #4	$103.76	7.111%	$111.1384	$111.14	$111.15	$111.10
Purchase #5	$95.28	10.500%	$105.2844	$105.28	$105.30	$105.30
Purchase #6	$169.72	5.311%	$178.7338	$178.73	$178.75	$178.70
Purchase #7	$124.68	4.185%	$129.8979	$129.90	$129.90	$129.90
7 purchase totals =	$621.50		$666.6296	$666.63	$666.70	$666.60