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	$245.88	10.213%	$270.9917	$270.99	$271.00	$271.00
Purchase #2	$109.59	5.674%	$115.8081	$115.81	$115.80	$115.80
Purchase #3	$83.41	7.262%	$89.4672	$89.47	$89.45	$89.50
Purchase #4	$222.32	10.160%	$244.9077	$244.91	$244.90	$244.90
Purchase #5	$60.57	8.857%	$65.9347	$65.93	$65.95	$65.90
Purchase #6	$50.85	7.175%	$54.4985	$54.50	$54.50	$54.50
Purchase #7	$162.43	6.454%	$172.9132	$172.91	$172.90	$172.90
7 purchase totals =	$935.05		$1,014.5211	$1,014.52	$1,014.50	$1,014.50