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	$20.35	4.453%	$21.2562	$21.26	$21.25	$21.30
Purchase #2	$50.93	4.378%	$53.1597	$53.16	$53.15	$53.20
Purchase #3	$35.53	12.144%	$39.8448	$39.84	$39.85	$39.80
Purchase #4	$75.95	5.416%	$80.0635	$80.06	$80.05	$80.10
Purchase #5	$37.62	3.409%	$38.9025	$38.90	$38.90	$38.90
Purchase #6	$105.67	10.259%	$116.5107	$116.51	$116.50	$116.50
Purchase #7	$95.85	3.359%	$99.0696	$99.07	$99.05	$99.10
7 purchase totals =	$421.90		$448.8070	$448.80	$448.75	$448.90