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	$142.30	3.156%	$146.791	$146.79	$146.80	$146.80
Purchase #2	$178.63	5.461%	$188.385	$188.39	$188.40	$188.40
Purchase #3	$135.90	6.743%	$145.0637	$145.06	$145.05	$145.10
Purchase #4	$70.63	10.522%	$78.0617	$78.06	$78.05	$78.10
Purchase #5	$183.48	13.620%	$208.47	$208.47	$208.45	$208.50
Purchase #6	$161.27	7.779%	$173.8152	$173.82	$173.80	$173.80
Purchase #7	$59.54	13.696%	$67.6946	$67.69	$67.70	$67.70
7 purchase totals =	$931.75		$1,008.2812	$1,008.28	$1,008.25	$1,008.40