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	$147.79	9.341%	$161.5951	$161.60	$161.60	$161.60
Purchase #2	$245.95	6.490%	$261.9122	$261.91	$261.90	$261.90
Purchase #3	$178.26	12.483%	$200.5122	$200.51	$200.50	$200.50
Purchase #4	$118.49	11.132%	$131.6803	$131.68	$131.70	$131.70
Purchase #5	$34.53	3.754%	$35.8263	$35.83	$35.85	$35.80
Purchase #6	$54.38	12.536%	$61.1971	$61.20	$61.20	$61.20
Purchase #7	$240.71	4.252%	$250.945	$250.95	$250.95	$250.90
7 purchase totals =	$1,020.11		$1,103.6682	$1,103.68	$1,103.70	$1,103.60