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	$63.84	6.323%	$67.8766	$67.88	$67.90	$67.90
Purchase #2	$53.69	7.533%	$57.7345	$57.73	$57.75	$57.70
Purchase #3	$250.61	12.705%	$282.45	$282.45	$282.45	$282.50
Purchase #4	$176.60	4.436%	$184.434	$184.43	$184.45	$184.40
Purchase #5	$44.68	13.723%	$50.8114	$50.81	$50.80	$50.80
Purchase #6	$99.73	3.236%	$102.9573	$102.96	$102.95	$103.00
Purchase #7	$173.61	12.482%	$195.28	$195.28	$195.30	$195.30
7 purchase totals =	$862.76		$941.5438	$941.54	$941.60	$941.60