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	$227.77	4.873%	$238.8692	$238.87	$238.85	$238.90
Purchase #2	$55.26	8.311%	$59.8527	$59.85	$59.85	$59.90
Purchase #3	$151.68	11.395%	$168.9639	$168.96	$168.95	$169.00
Purchase #4	$46.69	8.624%	$50.7165	$50.72	$50.70	$50.70
Purchase #5	$198.65	6.613%	$211.7867	$211.79	$211.80	$211.80
Purchase #6	$86.49	5.736%	$91.4511	$91.45	$91.45	$91.50
Purchase #7	$142.75	4.605%	$149.3236	$149.32	$149.30	$149.30
7 purchase totals =	$909.29		$970.9637	$970.96	$970.90	$971.10