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	$227.70	6.350%	$242.159	$242.16	$242.15	$242.20
Purchase #2	$60.27	11.383%	$67.1305	$67.13	$67.15	$67.10
Purchase #3	$138.93	12.586%	$156.4157	$156.42	$156.40	$156.40
Purchase #4	$119.57	6.368%	$127.1842	$127.18	$127.20	$127.20
Purchase #5	$20.88	10.654%	$23.1046	$23.10	$23.10	$23.10
Purchase #6	$209.49	7.300%	$224.7828	$224.78	$224.80	$224.80
Purchase #7	$91.27	9.791%	$100.2062	$100.21	$100.20	$100.20
7 purchase totals =	$868.11		$940.9830	$940.98	$941.00	$941.00