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	$55.99	3.229%	$57.7979	$57.80	$57.80	$57.80
Purchase #2	$48.30	7.789%	$52.0621	$52.06	$52.05	$52.10
Purchase #3	$241.85	4.849%	$253.5773	$253.58	$253.60	$253.60
Purchase #4	$162.72	10.103%	$179.1596	$179.16	$179.15	$179.20
Purchase #5	$179.34	4.801%	$187.9501	$187.95	$187.95	$188.00
Purchase #6	$56.77	4.602%	$59.3826	$59.38	$59.40	$59.40
Purchase #7	$180.46	4.740%	$189.0138	$189.01	$189.00	$189.00
7 purchase totals =	$925.43		$978.9434	$978.94	$978.95	$979.10