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	$71.40	8.596%	$77.5375	$77.54	$77.55	$77.50
Purchase #2	$110.39	3.194%	$113.9159	$113.92	$113.90	$113.90
Purchase #3	$179.72	3.270%	$185.5968	$185.60	$185.60	$185.60
Purchase #4	$55.38	4.325%	$57.7752	$57.78	$57.80	$57.80
Purchase #5	$91.41	11.828%	$102.222	$102.22	$102.20	$102.20
Purchase #6	$54.29	8.215%	$58.7499	$58.75	$58.75	$58.70
Purchase #7	$121.32	4.771%	$127.1082	$127.11	$127.10	$127.10
7 purchase totals =	$683.91		$722.9055	$722.92	$722.90	$722.80