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	$157.68	6.114%	$167.3206	$167.32	$167.30	$167.30
Purchase #2	$108.84	3.646%	$112.8083	$112.81	$112.80	$112.80
Purchase #3	$163.52	13.420%	$185.4644	$185.46	$185.45	$185.50
Purchase #4	$81.68	5.847%	$86.4558	$86.46	$86.45	$86.50
Purchase #5	$176.80	3.413%	$182.8342	$182.83	$182.85	$182.80
Purchase #6	$234.44	8.580%	$254.555	$254.56	$254.55	$254.60
Purchase #7	$28.86	8.496%	$31.3119	$31.31	$31.30	$31.30
7 purchase totals =	$951.82		$1,020.7502	$1,020.75	$1,020.70	$1,020.80