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	$67.89	7.432%	$72.9356	$72.94	$72.95	$72.90
Purchase #2	$96.34	10.102%	$106.0723	$106.07	$106.05	$106.10
Purchase #3	$154.80	9.561%	$169.6004	$169.60	$169.60	$169.60
Purchase #4	$117.30	12.325%	$131.7572	$131.76	$131.75	$131.80
Purchase #5	$95.93	7.746%	$103.3607	$103.36	$103.35	$103.40
Purchase #6	$174.40	4.257%	$181.8242	$181.82	$181.80	$181.80
Purchase #7	$96.30	8.747%	$104.7234	$104.72	$104.70	$104.70
7 purchase totals =	$802.96		$870.2738	$870.27	$870.20	$870.30