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	$75.62	3.506%	$78.2712	$78.27	$78.25	$78.30
Purchase #2	$177.61	10.387%	$196.0584	$196.06	$196.05	$196.10
Purchase #3	$56.65	5.592%	$59.8179	$59.82	$59.80	$59.80
Purchase #4	$83.77	10.635%	$92.6789	$92.68	$92.70	$92.70
Purchase #5	$14.78	3.405%	$15.2833	$15.28	$15.30	$15.30
Purchase #6	$5.26	12.431%	$5.9139	$5.91	$5.90	$5.90
Purchase #7	$236.28	8.433%	$256.2055	$256.21	$256.20	$256.20
7 purchase totals =	$649.97		$704.2291	$704.23	$704.20	$704.30