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	$170.33	9.162%	$185.9356	$185.94	$185.95	$185.90
Purchase #2	$112.53	3.733%	$116.7307	$116.73	$116.75	$116.70
Purchase #3	$124.34	9.632%	$136.3164	$136.32	$136.30	$136.30
Purchase #4	$101.43	7.358%	$108.8932	$108.89	$108.90	$108.90
Purchase #5	$57.28	7.805%	$61.7507	$61.75	$61.75	$61.80
Purchase #6	$48.35	7.856%	$52.1484	$52.15	$52.15	$52.10
Purchase #7	$92.77	5.763%	$98.1163	$98.12	$98.10	$98.10
7 purchase totals =	$707.03		$759.8913	$759.90	$759.90	$759.80