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	$54.66	6.204%	$58.0511	$58.05	$58.05	$58.10
Purchase #2	$137.83	6.206%	$146.3837	$146.38	$146.40	$146.40
Purchase #3	$225.97	9.617%	$247.7015	$247.70	$247.70	$247.70
Purchase #4	$160.40	6.703%	$171.1516	$171.15	$171.15	$171.20
Purchase #5	$164.61	9.687%	$180.5558	$180.56	$180.55	$180.60
Purchase #6	$128.27	4.161%	$133.6073	$133.61	$133.60	$133.60
Purchase #7	$167.65	10.702%	$185.5919	$185.59	$185.60	$185.60
7 purchase totals =	$1,039.39		$1,123.0429	$1,123.04	$1,123.05	$1,123.20