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	$168.83	8.431%	$183.0641	$183.06	$183.05	$183.10
Purchase #2	$36.53	13.233%	$41.364	$41.36	$41.35	$41.40
Purchase #3	$139.58	13.408%	$158.2949	$158.29	$158.30	$158.30
Purchase #4	$102.51	11.470%	$114.2679	$114.27	$114.25	$114.30
Purchase #5	$45.59	10.690%	$50.4636	$50.46	$50.45	$50.50
Purchase #6	$12.29	9.748%	$13.488	$13.49	$13.50	$13.50
Purchase #7	$105.40	6.858%	$112.6283	$112.63	$112.65	$112.60
7 purchase totals =	$610.73		$673.5708	$673.56	$673.55	$673.70