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	$34.49	13.855%	$39.2686	$39.27	$39.25	$39.30
Purchase #2	$179.27	3.326%	$185.2325	$185.23	$185.25	$185.20
Purchase #3	$199.53	7.167%	$213.8303	$213.83	$213.85	$213.80
Purchase #4	$165.31	10.503%	$182.6725	$182.67	$182.65	$182.70
Purchase #5	$116.70	9.287%	$127.5379	$127.54	$127.55	$127.50
Purchase #6	$59.84	7.777%	$64.4938	$64.49	$64.50	$64.50
Purchase #7	$170.46	8.152%	$184.3559	$184.36	$184.35	$184.40
7 purchase totals =	$925.60		$997.3915	$997.39	$997.40	$997.40