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	$80.55	3.472%	$83.3467	$83.35	$83.35	$83.30
Purchase #2	$82.64	9.691%	$90.6486	$90.65	$90.65	$90.60
Purchase #3	$65.30	8.514%	$70.8596	$70.86	$70.85	$70.90
Purchase #4	$42.90	13.595%	$48.7323	$48.73	$48.75	$48.70
Purchase #5	$161.32	11.612%	$180.0525	$180.05	$180.05	$180.10
Purchase #6	$188.94	5.272%	$198.9009	$198.90	$198.90	$198.90
Purchase #7	$154.33	13.433%	$175.0611	$175.06	$175.05	$175.10
7 purchase totals =	$775.98		$847.6017	$847.60	$847.60	$847.60