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	$41.45	6.676%	$44.2172	$44.22	$44.20	$44.20
Purchase #2	$63.29	3.133%	$65.2729	$65.27	$65.25	$65.30
Purchase #3	$129.98	11.864%	$145.4008	$145.40	$145.40	$145.40
Purchase #4	$143.81	6.812%	$153.6063	$153.61	$153.60	$153.60
Purchase #5	$135.81	6.417%	$144.5249	$144.52	$144.50	$144.50
Purchase #6	$124.92	7.675%	$134.5076	$134.51	$134.50	$134.50
Purchase #7	$137.34	7.395%	$147.4963	$147.50	$147.50	$147.50
7 purchase totals =	$776.60		$835.0260	$835.03	$834.95	$835.00