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	$48.82	13.794%	$55.5542	$55.55	$55.55	$55.60
Purchase #2	$52.25	3.833%	$54.2527	$54.25	$54.25	$54.30
Purchase #3	$27.42	3.854%	$28.4768	$28.48	$28.50	$28.50
Purchase #4	$67.84	3.656%	$70.3202	$70.32	$70.30	$70.30
Purchase #5	$92.85	12.294%	$104.265	$104.27	$104.25	$104.30
Purchase #6	$169.43	11.509%	$188.9297	$188.93	$188.95	$188.90
Purchase #7	$83.74	9.462%	$91.6635	$91.66	$91.65	$91.70
7 purchase totals =	$542.35		$593.4621	$593.46	$593.45	$593.60