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	$43.77	4.658%	$45.8088	$45.81	$45.80	$45.80
Purchase #2	$24.69	13.852%	$28.1101	$28.11	$28.10	$28.10
Purchase #3	$104.58	6.259%	$111.1257	$111.13	$111.15	$111.10
Purchase #4	$79.67	3.285%	$82.2872	$82.29	$82.30	$82.30
Purchase #5	$14.45	6.274%	$15.3566	$15.36	$15.35	$15.40
Purchase #6	$175.46	4.511%	$183.375	$183.38	$183.40	$183.40
Purchase #7	$35.34	5.680%	$37.3473	$37.35	$37.35	$37.30
7 purchase totals =	$477.96		$503.4107	$503.43	$503.45	$503.40