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	$179.37	3.616%	$185.856	$185.86	$185.85	$185.90
Purchase #2	$185.45	13.610%	$210.6897	$210.69	$210.70	$210.70
Purchase #3	$90.70	11.747%	$101.3545	$101.35	$101.35	$101.40
Purchase #4	$71.49	11.677%	$79.8379	$79.84	$79.85	$79.80
Purchase #5	$119.48	3.483%	$123.6415	$123.64	$123.65	$123.60
Purchase #6	$200.72	7.333%	$215.4388	$215.44	$215.45	$215.40
Purchase #7	$122.39	10.258%	$134.9448	$134.94	$134.95	$134.90
7 purchase totals =	$969.60		$1,051.7632	$1,051.76	$1,051.80	$1,051.70