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	$223.56	10.712%	$247.5077	$247.51	$247.50	$247.50
Purchase #2	$250.92	11.318%	$279.3191	$279.32	$279.30	$279.30
Purchase #3	$145.95	4.451%	$152.4462	$152.45	$152.45	$152.40
Purchase #4	$165.92	9.873%	$182.3013	$182.30	$182.30	$182.30
Purchase #5	$116.33	12.689%	$131.0911	$131.09	$131.10	$131.10
Purchase #6	$62.88	3.874%	$65.316	$65.32	$65.30	$65.30
Purchase #7	$23.51	13.685%	$26.7273	$26.73	$26.75	$26.70
7 purchase totals =	$989.07		$1,084.7087	$1,084.72	$1,084.70	$1,084.60