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	$158.31	6.136%	$168.0239	$168.02	$168.00	$168.00
Purchase #2	$45.53	5.301%	$47.9435	$47.94	$47.95	$47.90
Purchase #3	$63.50	3.544%	$65.7504	$65.75	$65.75	$65.80
Purchase #4	$45.53	10.527%	$50.3229	$50.32	$50.30	$50.30
Purchase #5	$81.29	8.735%	$88.3907	$88.39	$88.40	$88.40
Purchase #6	$153.88	8.662%	$167.2091	$167.21	$167.20	$167.20
Purchase #7	$196.65	13.182%	$222.5724	$222.57	$222.55	$222.60
7 purchase totals =	$744.69		$810.2129	$810.20	$810.15	$810.20