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	$48.84	13.273%	$55.3225	$55.32	$55.30	$55.30
Purchase #2	$59.95	10.223%	$66.0787	$66.08	$66.10	$66.10
Purchase #3	$90.56	9.714%	$99.357	$99.36	$99.35	$99.40
Purchase #4	$88.43	8.409%	$95.8661	$95.87	$95.85	$95.90
Purchase #5	$47.70	11.613%	$53.2394	$53.24	$53.25	$53.20
Purchase #6	$102.30	11.858%	$114.4307	$114.43	$114.45	$114.40
Purchase #7	$52.77	12.849%	$59.5504	$59.55	$59.55	$59.60
7 purchase totals =	$490.55		$543.8448	$543.85	$543.85	$543.90