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	$100.69	3.636%	$104.3511	$104.35	$104.35	$104.40
Purchase #2	$89.98	10.736%	$99.6403	$99.64	$99.65	$99.60
Purchase #3	$99.40	12.354%	$111.6799	$111.68	$111.70	$111.70
Purchase #4	$164.51	12.553%	$185.1609	$185.16	$185.15	$185.20
Purchase #5	$155.75	4.522%	$162.793	$162.79	$162.80	$162.80
Purchase #6	$63.51	3.280%	$65.5931	$65.59	$65.60	$65.60
Purchase #7	$111.48	3.425%	$115.2982	$115.30	$115.30	$115.30
7 purchase totals =	$785.32		$844.5165	$844.51	$844.55	$844.60