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	$240.87	11.663%	$268.9627	$268.96	$268.95	$269.00
Purchase #2	$229.69	11.159%	$255.3211	$255.32	$255.30	$255.30
Purchase #3	$74.57	11.848%	$83.4051	$83.41	$83.40	$83.40
Purchase #4	$28.93	12.371%	$32.5089	$32.51	$32.50	$32.50
Purchase #5	$95.77	3.453%	$99.0769	$99.08	$99.10	$99.10
Purchase #6	$111.71	4.507%	$116.7448	$116.74	$116.75	$116.70
Purchase #7	$77.76	5.291%	$81.8743	$81.87	$81.85	$81.90
7 purchase totals =	$859.30		$937.8938	$937.89	$937.85	$937.90