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	$127.92	7.793%	$137.8888	$137.89	$137.90	$137.90
Purchase #2	$118.41	12.574%	$133.2989	$133.30	$133.30	$133.30
Purchase #3	$130.25	10.561%	$144.0057	$144.01	$144.00	$144.00
Purchase #4	$136.63	5.304%	$143.8769	$143.88	$143.90	$143.90
Purchase #5	$36.67	4.519%	$38.3271	$38.33	$38.35	$38.30
Purchase #6	$151.86	5.508%	$160.2244	$160.22	$160.20	$160.20
Purchase #7	$218.69	10.737%	$242.1707	$242.17	$242.15	$242.20
7 purchase totals =	$920.43		$999.7925	$999.80	$999.80	$999.80