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	$58.91	3.551%	$61.0019	$61.00	$61.00	$61.00
Purchase #2	$82.76	9.707%	$90.7935	$90.79	$90.80	$90.80
Purchase #3	$174.70	6.439%	$185.9489	$185.95	$185.95	$185.90
Purchase #4	$34.66	11.558%	$38.666	$38.67	$38.65	$38.70
Purchase #5	$124.59	9.322%	$136.2043	$136.20	$136.20	$136.20
Purchase #6	$175.74	11.314%	$195.6232	$195.62	$195.60	$195.60
Purchase #7	$128.57	9.517%	$140.806	$140.81	$140.80	$140.80
7 purchase totals =	$779.93		$849.0438	$849.04	$849.00	$849.00