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	$183.61	11.278%	$204.3175	$204.32	$204.30	$204.30
Purchase #2	$116.90	8.571%	$126.9195	$126.92	$126.90	$126.90
Purchase #3	$37.43	13.618%	$42.5272	$42.53	$42.55	$42.50
Purchase #4	$151.87	6.558%	$161.8296	$161.83	$161.85	$161.80
Purchase #5	$203.26	4.625%	$212.6608	$212.66	$212.65	$212.70
Purchase #6	$49.53	6.222%	$52.6118	$52.61	$52.60	$52.60
Purchase #7	$112.43	13.280%	$127.3607	$127.36	$127.35	$127.40
7 purchase totals =	$855.03		$928.2271	$928.23	$928.20	$928.20