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	$247.67	4.814%	$259.5928	$259.59	$259.60	$259.60
Purchase #2	$249.25	7.699%	$268.4398	$268.44	$268.45	$268.40
Purchase #3	$57.53	7.602%	$61.9034	$61.90	$61.90	$61.90
Purchase #4	$64.86	10.773%	$71.8474	$71.85	$71.85	$71.80
Purchase #5	$85.43	4.738%	$89.4777	$89.48	$89.50	$89.50
Purchase #6	$7.43	12.346%	$8.3473	$8.35	$8.35	$8.30
Purchase #7	$113.72	7.261%	$121.9772	$121.98	$122.00	$122.00
7 purchase totals =	$825.89		$881.5856	$881.59	$881.65	$881.50