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	$117.62	5.777%	$124.4149	$124.41	$124.40	$124.40
Purchase #2	$220.50	7.700%	$237.4785	$237.48	$237.50	$237.50
Purchase #3	$106.94	8.564%	$116.0983	$116.10	$116.10	$116.10
Purchase #4	$92.88	12.257%	$104.2643	$104.26	$104.25	$104.30
Purchase #5	$101.33	10.118%	$111.5826	$111.58	$111.60	$111.60
Purchase #6	$78.99	4.212%	$82.3171	$82.32	$82.30	$82.30
Purchase #7	$37.67	10.313%	$41.5549	$41.55	$41.55	$41.60
7 purchase totals =	$755.93		$817.7106	$817.70	$817.70	$817.80