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	$98.28	11.697%	$109.7758	$109.78	$109.80	$109.80
Purchase #2	$160.73	7.537%	$172.8442	$172.84	$172.85	$172.80
Purchase #3	$163.36	7.299%	$175.2836	$175.28	$175.30	$175.30
Purchase #4	$105.40	5.404%	$111.0958	$111.10	$111.10	$111.10
Purchase #5	$213.86	7.402%	$229.6899	$229.69	$229.70	$229.70
Purchase #6	$158.38	12.852%	$178.735	$178.74	$178.75	$178.70
Purchase #7	$232.28	12.393%	$261.0665	$261.07	$261.05	$261.10
7 purchase totals =	$1,132.29		$1,238.4908	$1,238.50	$1,238.55	$1,238.50