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	$40.43	6.707%	$43.1416	$43.14	$43.15	$43.10
Purchase #2	$52.33	4.410%	$54.6378	$54.64	$54.65	$54.60
Purchase #3	$140.30	13.642%	$159.4397	$159.44	$159.45	$159.40
Purchase #4	$168.88	6.612%	$180.0463	$180.05	$180.05	$180.00
Purchase #5	$11.77	6.402%	$12.5235	$12.52	$12.50	$12.50
Purchase #6	$237.67	8.773%	$258.5208	$258.52	$258.50	$258.50
Purchase #7	$195.42	11.575%	$218.0399	$218.04	$218.05	$218.00
7 purchase totals =	$846.80		$926.3496	$926.35	$926.35	$926.10