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	$94.51	5.183%	$99.4085	$99.41	$99.40	$99.40
Purchase #2	$130.51	10.843%	$144.6612	$144.66	$144.65	$144.70
Purchase #3	$34.45	10.573%	$38.0924	$38.09	$38.10	$38.10
Purchase #4	$92.87	6.626%	$99.0236	$99.02	$99.00	$99.00
Purchase #5	$152.44	13.432%	$172.9157	$172.92	$172.90	$172.90
Purchase #6	$87.62	12.614%	$98.6724	$98.67	$98.65	$98.70
Purchase #7	$112.27	9.523%	$122.9615	$122.96	$122.95	$123.00
7 purchase totals =	$704.67		$775.7353	$775.73	$775.65	$775.80