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	$72.89	9.514%	$79.8248	$79.82	$79.80	$79.80
Purchase #2	$12.32	3.697%	$12.7755	$12.78	$12.80	$12.80
Purchase #3	$15.97	13.230%	$18.0828	$18.08	$18.10	$18.10
Purchase #4	$98.26	5.625%	$103.7871	$103.79	$103.80	$103.80
Purchase #5	$38.85	8.426%	$42.1235	$42.12	$42.10	$42.10
Purchase #6	$123.49	8.343%	$133.7928	$133.79	$133.80	$133.80
Purchase #7	$178.47	3.697%	$185.068	$185.07	$185.05	$185.10
7 purchase totals =	$540.25		$575.4545	$575.45	$575.45	$575.50