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	$67.98	13.509%	$77.1634	$77.16	$77.15	$77.20
Purchase #2	$85.26	4.859%	$89.4028	$89.40	$89.40	$89.40
Purchase #3	$28.63	3.440%	$29.6149	$29.61	$29.60	$29.60
Purchase #4	$173.96	10.320%	$191.9127	$191.91	$191.90	$191.90
Purchase #5	$32.45	3.277%	$33.5134	$33.51	$33.50	$33.50
Purchase #6	$9.63	9.118%	$10.5081	$10.51	$10.50	$10.50
Purchase #7	$159.54	4.192%	$166.2279	$166.23	$166.25	$166.20
7 purchase totals =	$557.45		$598.3432	$598.33	$598.30	$598.30