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	$51.79	9.573%	$56.7479	$56.75	$56.75	$56.70
Purchase #2	$151.59	3.276%	$156.5561	$156.56	$156.55	$156.60
Purchase #3	$91.82	11.675%	$102.54	$102.54	$102.55	$102.50
Purchase #4	$120.28	9.501%	$131.7078	$131.71	$131.70	$131.70
Purchase #5	$133.79	11.570%	$149.2695	$149.27	$149.25	$149.30
Purchase #6	$72.26	5.342%	$76.1201	$76.12	$76.10	$76.10
Purchase #7	$115.37	11.530%	$128.6722	$128.67	$128.65	$128.70
7 purchase totals =	$736.90		$801.6136	$801.62	$801.55	$801.60