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	$89.57	11.154%	$99.5606	$99.56	$99.55	$99.60
Purchase #2	$191.89	5.527%	$202.4958	$202.50	$202.50	$202.50
Purchase #3	$9.57	12.422%	$10.7588	$10.76	$10.75	$10.80
Purchase #4	$147.96	11.397%	$164.823	$164.82	$164.80	$164.80
Purchase #5	$98.33	6.616%	$104.8355	$104.84	$104.85	$104.80
Purchase #6	$11.58	4.170%	$12.0629	$12.06	$12.05	$12.10
Purchase #7	$12.69	13.243%	$14.3705	$14.37	$14.35	$14.40
7 purchase totals =	$561.59		$608.9071	$608.91	$608.85	$609.00