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	$75.25	7.191%	$80.6612	$80.66	$80.65	$80.70
Purchase #2	$209.28	12.116%	$234.6364	$234.64	$234.65	$234.60
Purchase #3	$243.80	11.121%	$270.913	$270.91	$270.90	$270.90
Purchase #4	$41.40	5.654%	$43.7408	$43.74	$43.75	$43.70
Purchase #5	$209.43	9.852%	$230.063	$230.06	$230.05	$230.10
Purchase #6	$250.43	3.380%	$258.8945	$258.89	$258.90	$258.90
Purchase #7	$84.45	7.277%	$90.5954	$90.60	$90.60	$90.60
7 purchase totals =	$1,114.04		$1,209.5043	$1,209.50	$1,209.50	$1,209.50