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	$243.53	7.769%	$262.4498	$262.45	$262.45	$262.40
Purchase #2	$90.62	9.367%	$99.1084	$99.11	$99.10	$99.10
Purchase #3	$156.86	10.250%	$172.9382	$172.94	$172.95	$172.90
Purchase #4	$11.49	3.766%	$11.9227	$11.92	$11.90	$11.90
Purchase #5	$127.63	4.596%	$133.4959	$133.50	$133.50	$133.50
Purchase #6	$249.78	11.474%	$278.4398	$278.44	$278.45	$278.40
Purchase #7	$243.58	7.229%	$261.1884	$261.19	$261.20	$261.20
7 purchase totals =	$1,123.49		$1,219.5432	$1,219.55	$1,219.55	$1,219.40