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	$30.97	8.776%	$33.6879	$33.69	$33.70	$33.70
Purchase #2	$195.86	13.111%	$221.5392	$221.54	$221.55	$221.50
Purchase #3	$176.30	5.414%	$185.8449	$185.84	$185.85	$185.80
Purchase #4	$64.65	11.825%	$72.2949	$72.29	$72.30	$72.30
Purchase #5	$74.25	5.279%	$78.1697	$78.17	$78.15	$78.20
Purchase #6	$14.76	7.140%	$15.8139	$15.81	$15.80	$15.80
Purchase #7	$162.72	7.147%	$174.3496	$174.35	$174.35	$174.30
7 purchase totals =	$719.51		$781.7001	$781.69	$781.70	$781.60