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	$47.71	10.117%	$52.5368	$52.54	$52.55	$52.50
Purchase #2	$36.69	12.638%	$41.3269	$41.33	$41.35	$41.30
Purchase #3	$106.41	7.693%	$114.5961	$114.60	$114.60	$114.60
Purchase #4	$152.47	3.791%	$158.2501	$158.25	$158.25	$158.30
Purchase #5	$93.65	3.644%	$97.0626	$97.06	$97.05	$97.10
Purchase #6	$127.53	9.225%	$139.2946	$139.29	$139.30	$139.30
Purchase #7	$30.36	10.522%	$33.5545	$33.55	$33.55	$33.60
7 purchase totals =	$594.82		$636.6216	$636.62	$636.65	$636.70