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	$42.54	13.676%	$48.3578	$48.36	$48.35	$48.40
Purchase #2	$108.87	8.837%	$118.4908	$118.49	$118.50	$118.50
Purchase #3	$106.28	7.650%	$114.4104	$114.41	$114.40	$114.40
Purchase #4	$150.72	8.232%	$163.1273	$163.13	$163.15	$163.10
Purchase #5	$116.50	13.151%	$131.8209	$131.82	$131.80	$131.80
Purchase #6	$59.34	13.867%	$67.5687	$67.57	$67.55	$67.60
Purchase #7	$63.75	10.690%	$70.5649	$70.56	$70.55	$70.60
7 purchase totals =	$648.00		$714.3408	$714.34	$714.30	$714.40