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	$82.45	7.760%	$88.8481	$88.85	$88.85	$88.80
Purchase #2	$220.92	13.561%	$250.879	$250.88	$250.90	$250.90
Purchase #3	$58.42	12.521%	$65.7348	$65.73	$65.75	$65.70
Purchase #4	$38.51	12.827%	$43.4497	$43.45	$43.45	$43.40
Purchase #5	$51.97	4.605%	$54.3632	$54.36	$54.35	$54.40
Purchase #6	$101.57	7.478%	$109.1654	$109.17	$109.15	$109.20
Purchase #7	$64.30	7.492%	$69.1174	$69.12	$69.10	$69.10
7 purchase totals =	$618.14		$681.5576	$681.56	$681.55	$681.50