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	$213.41	12.310%	$239.6808	$239.68	$239.70	$239.70
Purchase #2	$89.46	12.555%	$100.6917	$100.69	$100.70	$100.70
Purchase #3	$51.72	5.304%	$54.4632	$54.46	$54.45	$54.50
Purchase #4	$41.81	3.264%	$43.1747	$43.17	$43.15	$43.20
Purchase #5	$76.31	7.553%	$82.0737	$82.07	$82.05	$82.10
Purchase #6	$183.94	12.741%	$207.3758	$207.38	$207.40	$207.40
Purchase #7	$80.61	11.229%	$89.6617	$89.66	$89.65	$89.70
7 purchase totals =	$737.26		$817.1216	$817.11	$817.10	$817.30