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	$25.58	11.840%	$28.6087	$28.61	$28.60	$28.60
Purchase #2	$245.51	5.113%	$258.0629	$258.06	$258.05	$258.10
Purchase #3	$62.92	13.506%	$71.418	$71.42	$71.40	$71.40
Purchase #4	$114.98	11.244%	$127.9084	$127.91	$127.90	$127.90
Purchase #5	$42.96	11.771%	$48.0168	$48.02	$48.00	$48.00
Purchase #6	$124.53	9.758%	$136.6816	$136.68	$136.70	$136.70
Purchase #7	$135.69	9.767%	$148.9428	$148.94	$148.95	$148.90
7 purchase totals =	$752.17		$819.6392	$819.64	$819.60	$819.60