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	$142.83	5.531%	$150.7299	$150.73	$150.75	$150.70
Purchase #2	$59.32	8.778%	$64.5271	$64.53	$64.55	$64.50
Purchase #3	$122.64	8.648%	$133.2459	$133.25	$133.25	$133.20
Purchase #4	$82.79	8.613%	$89.9207	$89.92	$89.90	$89.90
Purchase #5	$207.59	8.274%	$224.766	$224.77	$224.75	$224.80
Purchase #6	$133.57	7.521%	$143.6158	$143.62	$143.60	$143.60
Purchase #7	$139.77	13.841%	$159.1156	$159.12	$159.10	$159.10
7 purchase totals =	$888.51		$965.9210	$965.94	$965.90	$965.80