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	$25.95	10.401%	$28.6491	$28.65	$28.65	$28.60
Purchase #2	$135.47	9.369%	$148.1622	$148.16	$148.15	$148.20
Purchase #3	$155.34	3.534%	$160.8297	$160.83	$160.85	$160.80
Purchase #4	$88.50	8.599%	$96.1101	$96.11	$96.10	$96.10
Purchase #5	$74.77	10.238%	$82.425	$82.43	$82.45	$82.40
Purchase #6	$196.91	7.695%	$212.0622	$212.06	$212.05	$212.10
Purchase #7	$113.38	12.558%	$127.6183	$127.62	$127.60	$127.60
7 purchase totals =	$790.32		$855.8566	$855.86	$855.85	$855.80