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	$80.72	6.606%	$86.0524	$86.05	$86.05	$86.10
Purchase #2	$122.88	10.268%	$135.4973	$135.50	$135.50	$135.50
Purchase #3	$134.56	3.515%	$139.2898	$139.29	$139.30	$139.30
Purchase #4	$127.67	12.315%	$143.3926	$143.39	$143.40	$143.40
Purchase #5	$178.64	10.190%	$196.8434	$196.84	$196.85	$196.80
Purchase #6	$80.81	10.870%	$89.594	$89.59	$89.60	$89.60
Purchase #7	$10.47	10.621%	$11.582	$11.58	$11.60	$11.60
7 purchase totals =	$735.75		$802.2515	$802.24	$802.30	$802.30