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	$204.77	5.602%	$216.2412	$216.24	$216.25	$216.20
Purchase #2	$133.84	10.822%	$148.3242	$148.32	$148.30	$148.30
Purchase #3	$204.67	3.785%	$212.4168	$212.42	$212.40	$212.40
Purchase #4	$97.32	8.125%	$105.2273	$105.23	$105.25	$105.20
Purchase #5	$167.94	8.150%	$181.6271	$181.63	$181.65	$181.60
Purchase #6	$116.54	11.216%	$129.6111	$129.61	$129.60	$129.60
Purchase #7	$91.92	9.274%	$100.4447	$100.44	$100.45	$100.40
7 purchase totals =	$1,017.00		$1,093.8924	$1,093.89	$1,093.90	$1,093.70