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	$95.86	9.822%	$105.2754	$105.28	$105.30	$105.30
Purchase #2	$105.96	11.617%	$118.2694	$118.27	$118.25	$118.30
Purchase #3	$111.39	8.726%	$121.1099	$121.11	$121.10	$121.10
Purchase #4	$64.98	10.698%	$71.9316	$71.93	$71.95	$71.90
Purchase #5	$94.25	10.623%	$104.2622	$104.26	$104.25	$104.30
Purchase #6	$28.66	12.856%	$32.3445	$32.34	$32.35	$32.30
Purchase #7	$138.77	3.870%	$144.1404	$144.14	$144.15	$144.10
7 purchase totals =	$639.87		$697.3334	$697.33	$697.35	$697.30