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	$106.83	12.586%	$120.2756	$120.28	$120.30	$120.30
Purchase #2	$191.61	5.389%	$201.9359	$201.94	$201.95	$201.90
Purchase #3	$11.58	11.291%	$12.8875	$12.89	$12.90	$12.90
Purchase #4	$182.84	9.116%	$199.5077	$199.51	$199.50	$199.50
Purchase #5	$33.97	7.669%	$36.5752	$36.58	$36.60	$36.60
Purchase #6	$83.29	7.209%	$89.2944	$89.29	$89.30	$89.30
Purchase #7	$57.56	6.752%	$61.4465	$61.45	$61.45	$61.40
7 purchase totals =	$667.68		$721.9228	$721.94	$722.00	$721.90