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	$130.77	13.379%	$148.2657	$148.27	$148.25	$148.30
Purchase #2	$171.38	11.467%	$191.0321	$191.03	$191.05	$191.00
Purchase #3	$83.85	6.272%	$89.1091	$89.11	$89.10	$89.10
Purchase #4	$108.80	7.254%	$116.6924	$116.69	$116.70	$116.70
Purchase #5	$69.85	9.409%	$76.4222	$76.42	$76.40	$76.40
Purchase #6	$64.67	12.232%	$72.5804	$72.58	$72.60	$72.60
Purchase #7	$146.98	4.730%	$153.9322	$153.93	$153.95	$153.90
7 purchase totals =	$776.30		$848.0341	$848.03	$848.05	$848.00