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	$33.81	8.224%	$36.5905	$36.59	$36.60	$36.60
Purchase #2	$33.61	4.216%	$35.027	$35.03	$35.05	$35.00
Purchase #3	$63.70	12.313%	$71.5434	$71.54	$71.55	$71.50
Purchase #4	$127.45	5.715%	$134.7338	$134.73	$134.75	$134.70
Purchase #5	$80.84	11.790%	$90.371	$90.37	$90.35	$90.40
Purchase #6	$95.71	8.174%	$103.5333	$103.53	$103.55	$103.50
Purchase #7	$51.42	3.441%	$53.1894	$53.19	$53.20	$53.20
7 purchase totals =	$486.54		$524.9884	$524.98	$525.05	$524.90