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	$149.84	13.158%	$169.5559	$169.56	$169.55	$169.60
Purchase #2	$154.93	6.203%	$164.5403	$164.54	$164.55	$164.50
Purchase #3	$218.87	4.347%	$228.3843	$228.38	$228.40	$228.40
Purchase #4	$93.98	6.795%	$100.3659	$100.37	$100.35	$100.40
Purchase #5	$51.33	10.302%	$56.618	$56.62	$56.60	$56.60
Purchase #6	$84.42	8.297%	$91.4243	$91.42	$91.40	$91.40
Purchase #7	$54.70	8.623%	$59.4168	$59.42	$59.40	$59.40
7 purchase totals =	$808.07		$870.3055	$870.31	$870.25	$870.30