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	$16.41	12.779%	$18.507	$18.51	$18.50	$18.50
Purchase #2	$230.87	4.781%	$241.9079	$241.91	$241.90	$241.90
Purchase #3	$114.25	9.871%	$125.5276	$125.53	$125.55	$125.50
Purchase #4	$31.65	5.332%	$33.3376	$33.34	$33.35	$33.30
Purchase #5	$110.91	5.426%	$116.928	$116.93	$116.95	$116.90
Purchase #6	$43.85	10.809%	$48.5897	$48.59	$48.60	$48.60
Purchase #7	$138.88	5.807%	$146.9448	$146.94	$146.95	$146.90
7 purchase totals =	$686.82		$731.7426	$731.75	$731.80	$731.60