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	$79.83	12.245%	$89.6052	$89.61	$89.60	$89.60
Purchase #2	$193.27	3.335%	$199.7156	$199.72	$199.70	$199.70
Purchase #3	$127.29	11.231%	$141.5859	$141.59	$141.60	$141.60
Purchase #4	$181.46	8.201%	$196.3415	$196.34	$196.35	$196.30
Purchase #5	$104.46	12.480%	$117.4966	$117.50	$117.50	$117.50
Purchase #6	$237.69	3.170%	$245.2248	$245.22	$245.20	$245.20
Purchase #7	$162.68	12.874%	$183.6234	$183.62	$183.60	$183.60
7 purchase totals =	$1,086.68		$1,173.5930	$1,173.60	$1,173.55	$1,173.50