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	$160.88	11.192%	$178.8857	$178.89	$178.90	$178.90
Purchase #2	$243.52	7.630%	$262.1006	$262.10	$262.10	$262.10
Purchase #3	$167.48	10.623%	$185.2714	$185.27	$185.25	$185.30
Purchase #4	$120.83	8.507%	$131.109	$131.11	$131.10	$131.10
Purchase #5	$41.49	13.610%	$47.1368	$47.14	$47.15	$47.10
Purchase #6	$177.25	5.194%	$186.4564	$186.46	$186.45	$186.50
Purchase #7	$233.52	12.325%	$262.3013	$262.30	$262.30	$262.30
7 purchase totals =	$1,144.97		$1,253.2612	$1,253.27	$1,253.25	$1,253.30