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	$75.92	5.751%	$80.2862	$80.29	$80.30	$80.30
Purchase #2	$39.85	5.706%	$42.1238	$42.12	$42.10	$42.10
Purchase #3	$233.32	8.198%	$252.4476	$252.45	$252.45	$252.40
Purchase #4	$201.83	9.841%	$221.6921	$221.69	$221.70	$221.70
Purchase #5	$140.49	9.222%	$153.446	$153.45	$153.45	$153.40
Purchase #6	$83.38	3.561%	$86.3492	$86.35	$86.35	$86.30
Purchase #7	$71.66	9.552%	$78.505	$78.51	$78.50	$78.50
7 purchase totals =	$846.45		$914.8499	$914.86	$914.85	$914.70