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	$124.52	5.473%	$131.335	$131.34	$131.35	$131.30
Purchase #2	$52.40	9.302%	$57.2742	$57.27	$57.25	$57.30
Purchase #3	$57.57	8.839%	$62.6586	$62.66	$62.65	$62.70
Purchase #4	$116.46	11.869%	$130.2826	$130.28	$130.30	$130.30
Purchase #5	$116.45	12.865%	$131.4313	$131.43	$131.45	$131.40
Purchase #6	$237.56	12.177%	$266.4877	$266.49	$266.50	$266.50
Purchase #7	$38.54	7.481%	$41.4232	$41.42	$41.40	$41.40
7 purchase totals =	$743.50		$820.8926	$820.89	$820.90	$820.90