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	$240.44	5.367%	$253.3444	$253.34	$253.35	$253.30
Purchase #2	$244.74	4.553%	$255.883	$255.88	$255.90	$255.90
Purchase #3	$39.80	3.387%	$41.148	$41.15	$41.15	$41.10
Purchase #4	$52.28	3.131%	$53.9169	$53.92	$53.90	$53.90
Purchase #5	$131.32	5.527%	$138.5781	$138.58	$138.60	$138.60
Purchase #6	$85.27	6.190%	$90.5482	$90.55	$90.55	$90.50
Purchase #7	$67.31	6.242%	$71.5115	$71.51	$71.50	$71.50
7 purchase totals =	$861.16		$904.9301	$904.93	$904.95	$904.80