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	$246.80	12.627%	$277.9634	$277.96	$277.95	$278.00
Purchase #2	$133.86	4.420%	$139.7766	$139.78	$139.80	$139.80
Purchase #3	$143.37	13.174%	$162.2576	$162.26	$162.25	$162.30
Purchase #4	$88.43	10.873%	$98.045	$98.05	$98.05	$98.00
Purchase #5	$187.52	12.872%	$211.6576	$211.66	$211.65	$211.70
Purchase #6	$78.93	3.196%	$81.4526	$81.45	$81.45	$81.50
Purchase #7	$35.37	13.424%	$40.1181	$40.12	$40.10	$40.10
7 purchase totals =	$914.28		$1,011.2709	$1,011.28	$1,011.25	$1,011.40