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	$127.48	5.810%	$134.8866	$134.89	$134.90	$134.90
Purchase #2	$204.76	11.599%	$228.5101	$228.51	$228.50	$228.50
Purchase #3	$81.66	4.218%	$85.1044	$85.10	$85.10	$85.10
Purchase #4	$24.82	7.151%	$26.5949	$26.59	$26.60	$26.60
Purchase #5	$93.58	9.221%	$102.209	$102.21	$102.20	$102.20
Purchase #6	$233.73	13.301%	$264.8184	$264.82	$264.80	$264.80
Purchase #7	$170.66	4.751%	$178.7681	$178.77	$178.75	$178.80
7 purchase totals =	$936.69		$1,020.8915	$1,020.89	$1,020.85	$1,020.90