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	$236.70	12.187%	$265.5466	$265.55	$265.55	$265.50
Purchase #2	$138.75	3.827%	$144.06	$144.06	$144.05	$144.10
Purchase #3	$63.31	6.386%	$67.353	$67.35	$67.35	$67.40
Purchase #4	$42.74	12.463%	$48.0667	$48.07	$48.05	$48.10
Purchase #5	$63.63	11.487%	$70.9392	$70.94	$70.95	$70.90
Purchase #6	$49.32	12.195%	$55.3346	$55.33	$55.35	$55.30
Purchase #7	$47.88	10.391%	$52.8552	$52.86	$52.85	$52.90
7 purchase totals =	$642.33		$704.1553	$704.16	$704.15	$704.20