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	$172.82	3.789%	$179.3681	$179.37	$179.35	$179.40
Purchase #2	$110.77	6.535%	$118.0088	$118.01	$118.00	$118.00
Purchase #3	$49.63	13.547%	$56.3534	$56.35	$56.35	$56.40
Purchase #4	$243.55	10.340%	$268.7331	$268.73	$268.75	$268.70
Purchase #5	$235.42	10.436%	$259.9884	$259.99	$260.00	$260.00
Purchase #6	$19.44	5.114%	$20.4342	$20.43	$20.45	$20.40
Purchase #7	$100.77	11.623%	$112.4825	$112.48	$112.50	$112.50
7 purchase totals =	$932.40		$1,015.3685	$1,015.36	$1,015.40	$1,015.40