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	$90.45	9.822%	$99.334	$99.33	$99.35	$99.30
Purchase #2	$205.69	7.847%	$221.8305	$221.83	$221.85	$221.80
Purchase #3	$147.86	7.137%	$158.4128	$158.41	$158.40	$158.40
Purchase #4	$245.87	6.206%	$261.1287	$261.13	$261.15	$261.10
Purchase #5	$232.38	10.452%	$256.6684	$256.67	$256.65	$256.70
Purchase #6	$50.36	7.338%	$54.0554	$54.06	$54.05	$54.10
Purchase #7	$147.37	7.780%	$158.8354	$158.84	$158.85	$158.80
7 purchase totals =	$1,119.98		$1,210.2652	$1,210.27	$1,210.30	$1,210.20