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	$93.38	12.467%	$105.0217	$105.02	$105.00	$105.00
Purchase #2	$38.73	9.866%	$42.5511	$42.55	$42.55	$42.60
Purchase #3	$212.91	6.406%	$226.549	$226.55	$226.55	$226.50
Purchase #4	$47.56	4.445%	$49.674	$49.67	$49.65	$49.70
Purchase #5	$49.89	7.609%	$53.6861	$53.69	$53.70	$53.70
Purchase #6	$64.37	10.691%	$71.2518	$71.25	$71.25	$71.30
Purchase #7	$228.33	13.491%	$259.134	$259.13	$259.15	$259.10
7 purchase totals =	$735.17		$807.8677	$807.86	$807.85	$807.90