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	$18.57	8.261%	$20.1041	$20.10	$20.10	$20.10
Purchase #2	$63.44	5.685%	$67.0466	$67.05	$67.05	$67.00
Purchase #3	$98.61	13.839%	$112.2566	$112.26	$112.25	$112.30
Purchase #4	$189.29	10.132%	$208.4689	$208.47	$208.45	$208.50
Purchase #5	$48.94	13.229%	$55.4143	$55.41	$55.40	$55.40
Purchase #6	$188.29	6.638%	$200.7887	$200.79	$200.80	$200.80
Purchase #7	$12.25	7.429%	$13.1601	$13.16	$13.15	$13.20
7 purchase totals =	$619.39		$677.2393	$677.24	$677.20	$677.30