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	$57.63	6.173%	$61.1875	$61.19	$61.20	$61.20
Purchase #2	$145.29	5.393%	$153.1255	$153.13	$153.15	$153.10
Purchase #3	$150.58	13.818%	$171.3871	$171.39	$171.40	$171.40
Purchase #4	$75.98	8.751%	$82.629	$82.63	$82.65	$82.60
Purchase #5	$151.92	8.113%	$164.2453	$164.25	$164.25	$164.20
Purchase #6	$42.99	3.204%	$44.3674	$44.37	$44.35	$44.40
Purchase #7	$112.38	13.678%	$127.7513	$127.75	$127.75	$127.80
7 purchase totals =	$736.77		$804.6931	$804.71	$804.75	$804.70