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	$229.92	7.592%	$247.3755	$247.38	$247.40	$247.40
Purchase #2	$110.89	11.509%	$123.6523	$123.65	$123.65	$123.70
Purchase #3	$167.69	12.473%	$188.606	$188.61	$188.60	$188.60
Purchase #4	$18.55	12.571%	$20.8819	$20.88	$20.90	$20.90
Purchase #5	$203.32	13.175%	$230.1074	$230.11	$230.10	$230.10
Purchase #6	$155.33	13.835%	$176.8199	$176.82	$176.80	$176.80
Purchase #7	$14.27	4.661%	$14.9351	$14.94	$14.95	$14.90
7 purchase totals =	$899.97		$1,002.3781	$1,002.39	$1,002.40	$1,002.40