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	$213.74	4.335%	$223.0056	$223.01	$223.00	$223.00
Purchase #2	$156.51	13.678%	$177.9174	$177.92	$177.90	$177.90
Purchase #3	$230.93	5.347%	$243.2778	$243.28	$243.30	$243.30
Purchase #4	$45.99	9.558%	$50.3857	$50.39	$50.40	$50.40
Purchase #5	$205.31	9.650%	$225.1224	$225.12	$225.10	$225.10
Purchase #6	$41.53	5.253%	$43.7116	$43.71	$43.70	$43.70
Purchase #7	$126.30	12.836%	$142.5119	$142.51	$142.50	$142.50
7 purchase totals =	$1,020.31		$1,105.9324	$1,105.94	$1,105.90	$1,105.90