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	$52.58	8.173%	$56.8774	$56.88	$56.90	$56.90
Purchase #2	$168.25	5.611%	$177.6905	$177.69	$177.70	$177.70
Purchase #3	$95.62	4.421%	$99.8474	$99.85	$99.85	$99.80
Purchase #4	$113.47	11.666%	$126.7074	$126.71	$126.70	$126.70
Purchase #5	$42.45	10.361%	$46.8482	$46.85	$46.85	$46.80
Purchase #6	$48.37	8.274%	$52.3721	$52.37	$52.35	$52.40
Purchase #7	$35.41	13.263%	$40.1064	$40.11	$40.10	$40.10
7 purchase totals =	$556.15		$600.4494	$600.46	$600.45	$600.40