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	$165.77	4.844%	$173.7999	$173.80	$173.80	$173.80
Purchase #2	$114.27	9.210%	$124.7943	$124.79	$124.80	$124.80
Purchase #3	$30.25	9.374%	$33.0856	$33.09	$33.10	$33.10
Purchase #4	$90.85	10.738%	$100.6055	$100.61	$100.60	$100.60
Purchase #5	$80.50	6.684%	$85.8806	$85.88	$85.90	$85.90
Purchase #6	$39.50	7.601%	$42.5024	$42.50	$42.50	$42.50
Purchase #7	$233.29	10.409%	$257.5732	$257.57	$257.55	$257.60
7 purchase totals =	$754.43		$818.2415	$818.24	$818.25	$818.30