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	$236.92	13.770%	$269.5439	$269.54	$269.55	$269.50
Purchase #2	$89.46	11.341%	$99.6057	$99.61	$99.60	$99.60
Purchase #3	$41.88	12.143%	$46.9655	$46.97	$46.95	$47.00
Purchase #4	$27.80	11.776%	$31.0737	$31.07	$31.05	$31.10
Purchase #5	$152.59	6.297%	$162.1986	$162.20	$162.20	$162.20
Purchase #6	$141.66	12.656%	$159.5885	$159.59	$159.60	$159.60
Purchase #7	$212.27	4.309%	$221.4167	$221.42	$221.40	$221.40
7 purchase totals =	$902.58		$990.3926	$990.40	$990.35	$990.40