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	$14.69	4.665%	$15.3753	$15.38	$15.40	$15.40
Purchase #2	$7.76	12.456%	$8.7266	$8.73	$8.75	$8.70
Purchase #3	$218.91	5.168%	$230.2233	$230.22	$230.20	$230.20
Purchase #4	$98.67	13.398%	$111.8898	$111.89	$111.90	$111.90
Purchase #5	$125.86	4.580%	$131.6244	$131.62	$131.60	$131.60
Purchase #6	$167.76	12.763%	$189.1712	$189.17	$189.15	$189.20
Purchase #7	$52.92	13.607%	$60.1208	$60.12	$60.10	$60.10
7 purchase totals =	$686.57		$747.1314	$747.13	$747.10	$747.10