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	$141.73	10.633%	$156.8002	$156.80	$156.80	$156.80
Purchase #2	$120.77	8.321%	$130.8193	$130.82	$130.80	$130.80
Purchase #3	$199.60	11.306%	$222.1668	$222.17	$222.15	$222.20
Purchase #4	$155.43	3.277%	$160.5234	$160.52	$160.50	$160.50
Purchase #5	$120.29	8.122%	$130.06	$130.06	$130.05	$130.10
Purchase #6	$104.93	10.840%	$116.3044	$116.30	$116.30	$116.30
Purchase #7	$236.86	5.625%	$250.1834	$250.18	$250.20	$250.20
7 purchase totals =	$1,079.61		$1,166.8575	$1,166.85	$1,166.80	$1,166.90