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	$82.50	6.595%	$87.9409	$87.94	$87.95	$87.90
Purchase #2	$96.25	3.671%	$99.7833	$99.78	$99.80	$99.80
Purchase #3	$107.83	7.385%	$115.7932	$115.79	$115.80	$115.80
Purchase #4	$142.82	5.245%	$150.3109	$150.31	$150.30	$150.30
Purchase #5	$23.34	9.314%	$25.5139	$25.51	$25.50	$25.50
Purchase #6	$100.34	10.624%	$111.0001	$111.00	$111.00	$111.00
Purchase #7	$28.36	10.574%	$31.3588	$31.36	$31.35	$31.40
7 purchase totals =	$581.44		$621.7011	$621.69	$621.70	$621.70