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	$53.33	4.121%	$55.5277	$55.53	$55.55	$55.50
Purchase #2	$233.81	8.653%	$254.0416	$254.04	$254.05	$254.00
Purchase #3	$57.98	12.800%	$65.4014	$65.40	$65.40	$65.40
Purchase #4	$26.98	7.573%	$29.0232	$29.02	$29.00	$29.00
Purchase #5	$160.67	6.827%	$171.6389	$171.64	$171.65	$171.60
Purchase #6	$51.86	7.738%	$55.8729	$55.87	$55.85	$55.90
Purchase #7	$195.30	10.161%	$215.1444	$215.14	$215.15	$215.10
7 purchase totals =	$779.93		$846.6501	$846.64	$846.65	$846.50