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	$72.75	7.730%	$78.3736	$78.37	$78.35	$78.40
Purchase #2	$59.91	12.194%	$67.2154	$67.22	$67.20	$67.20
Purchase #3	$189.85	11.230%	$211.1702	$211.17	$211.15	$211.20
Purchase #4	$117.37	5.667%	$124.0214	$124.02	$124.00	$124.00
Purchase #5	$249.33	3.547%	$258.1737	$258.17	$258.15	$258.20
Purchase #6	$80.37	7.651%	$86.5191	$86.52	$86.50	$86.50
Purchase #7	$63.25	5.338%	$66.6263	$66.63	$66.65	$66.60
7 purchase totals =	$832.83		$892.0997	$892.10	$892.00	$892.10