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	$219.61	12.571%	$247.2172	$247.22	$247.20	$247.20
Purchase #2	$61.69	9.184%	$67.3556	$67.36	$67.35	$67.40
Purchase #3	$95.76	8.726%	$104.116	$104.12	$104.10	$104.10
Purchase #4	$121.83	5.662%	$128.728	$128.73	$128.75	$128.70
Purchase #5	$61.36	10.696%	$67.9231	$67.92	$67.90	$67.90
Purchase #6	$79.52	12.772%	$89.6763	$89.68	$89.70	$89.70
Purchase #7	$248.46	12.502%	$279.5225	$279.52	$279.50	$279.50
7 purchase totals =	$888.23		$984.5387	$984.55	$984.50	$984.50