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	$77.45	3.124%	$79.8695	$79.87	$79.85	$79.90
Purchase #2	$115.56	13.619%	$131.2981	$131.30	$131.30	$131.30
Purchase #3	$68.51	3.846%	$71.1449	$71.14	$71.15	$71.10
Purchase #4	$75.42	4.144%	$78.5454	$78.55	$78.55	$78.50
Purchase #5	$230.26	13.674%	$261.7458	$261.75	$261.75	$261.70
Purchase #6	$63.49	13.660%	$72.1627	$72.16	$72.15	$72.20
Purchase #7	$108.57	9.860%	$119.275	$119.28	$119.30	$119.30
7 purchase totals =	$739.26		$814.0414	$814.05	$814.05	$814.00