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	$71.27	12.484%	$80.1673	$80.17	$80.15	$80.20
Purchase #2	$202.61	8.814%	$220.468	$220.47	$220.45	$220.50
Purchase #3	$127.81	11.195%	$142.1183	$142.12	$142.10	$142.10
Purchase #4	$83.91	4.336%	$87.5483	$87.55	$87.55	$87.50
Purchase #5	$31.75	7.594%	$34.1611	$34.16	$34.15	$34.20
Purchase #6	$229.31	5.773%	$242.5481	$242.55	$242.55	$242.50
Purchase #7	$54.36	12.864%	$61.3529	$61.35	$61.35	$61.40
7 purchase totals =	$801.02		$868.3640	$868.37	$868.30	$868.40