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	$24.73	4.820%	$25.922	$25.92	$25.90	$25.90
Purchase #2	$58.44	12.840%	$65.9437	$65.94	$65.95	$65.90
Purchase #3	$172.76	13.414%	$195.934	$195.93	$195.95	$195.90
Purchase #4	$193.67	3.559%	$200.5627	$200.56	$200.55	$200.60
Purchase #5	$65.37	13.591%	$74.2544	$74.25	$74.25	$74.30
Purchase #6	$37.76	13.397%	$42.8187	$42.82	$42.80	$42.80
Purchase #7	$36.49	12.225%	$40.9509	$40.95	$40.95	$41.00
7 purchase totals =	$589.22		$646.3864	$646.37	$646.35	$646.40