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	$203.90	9.161%	$222.5793	$222.58	$222.60	$222.60
Purchase #2	$130.89	6.161%	$138.9541	$138.95	$138.95	$139.00
Purchase #3	$85.99	6.177%	$91.3016	$91.30	$91.30	$91.30
Purchase #4	$68.37	3.839%	$70.9947	$70.99	$71.00	$71.00
Purchase #5	$120.82	5.631%	$127.6234	$127.62	$127.60	$127.60
Purchase #6	$152.31	3.802%	$158.1008	$158.10	$158.10	$158.10
Purchase #7	$12.61	9.722%	$13.8359	$13.84	$13.85	$13.80
7 purchase totals =	$774.89		$823.3898	$823.38	$823.40	$823.40