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	$36.75	7.245%	$39.4125	$39.41	$39.40	$39.40
Purchase #2	$196.35	4.678%	$205.5353	$205.54	$205.55	$205.50
Purchase #3	$67.90	5.231%	$71.4518	$71.45	$71.45	$71.50
Purchase #4	$26.80	5.529%	$28.2818	$28.28	$28.30	$28.30
Purchase #5	$143.46	11.860%	$160.4744	$160.47	$160.45	$160.50
Purchase #6	$156.48	11.139%	$173.9103	$173.91	$173.90	$173.90
Purchase #7	$128.73	4.670%	$134.7417	$134.74	$134.75	$134.70
7 purchase totals =	$756.47		$813.8078	$813.80	$813.80	$813.80