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	$101.27	9.851%	$111.2461	$111.25	$111.25	$111.20
Purchase #2	$242.41	9.294%	$264.9396	$264.94	$264.95	$264.90
Purchase #3	$56.86	5.213%	$59.8241	$59.82	$59.80	$59.80
Purchase #4	$38.31	4.168%	$39.9068	$39.91	$39.90	$39.90
Purchase #5	$74.25	10.690%	$82.1873	$82.19	$82.20	$82.20
Purchase #6	$139.54	13.169%	$157.916	$157.92	$157.90	$157.90
Purchase #7	$143.78	8.653%	$156.2213	$156.22	$156.20	$156.20
7 purchase totals =	$796.42		$872.2412	$872.25	$872.20	$872.10