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	$177.27	6.641%	$189.0425	$189.04	$189.05	$189.00
Purchase #2	$125.37	6.129%	$133.0539	$133.05	$133.05	$133.10
Purchase #3	$9.58	8.822%	$10.4251	$10.43	$10.45	$10.40
Purchase #4	$139.98	8.608%	$152.0295	$152.03	$152.05	$152.00
Purchase #5	$39.56	3.131%	$40.7986	$40.80	$40.80	$40.80
Purchase #6	$53.78	3.389%	$55.6026	$55.60	$55.60	$55.60
Purchase #7	$10.79	7.608%	$11.6109	$11.61	$11.60	$11.60
7 purchase totals =	$556.33		$592.5631	$592.56	$592.60	$592.50