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	$49.79	13.590%	$56.5565	$56.56	$56.55	$56.60
Purchase #2	$72.70	8.463%	$78.8526	$78.85	$78.85	$78.90
Purchase #3	$229.67	4.207%	$239.3322	$239.33	$239.35	$239.30
Purchase #4	$82.92	7.388%	$89.0461	$89.05	$89.05	$89.00
Purchase #5	$222.93	3.609%	$230.9755	$230.98	$231.00	$231.00
Purchase #6	$59.52	10.310%	$65.6565	$65.66	$65.65	$65.70
Purchase #7	$14.59	8.489%	$15.8285	$15.83	$15.85	$15.80
7 purchase totals =	$732.12		$776.2479	$776.26	$776.30	$776.30