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	$207.77	9.681%	$227.8842	$227.88	$227.90	$227.90
Purchase #2	$74.58	10.539%	$82.44	$82.44	$82.45	$82.40
Purchase #3	$43.52	4.651%	$45.5441	$45.54	$45.55	$45.50
Purchase #4	$128.85	12.605%	$145.0915	$145.09	$145.10	$145.10
Purchase #5	$171.70	7.608%	$184.7629	$184.76	$184.75	$184.80
Purchase #6	$131.76	8.263%	$142.6473	$142.65	$142.65	$142.60
Purchase #7	$135.42	13.394%	$153.5582	$153.56	$153.55	$153.60
7 purchase totals =	$893.60		$981.9282	$981.92	$981.95	$981.90