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	$22.65	13.476%	$25.7023	$25.70	$25.70	$25.70
Purchase #2	$44.87	3.108%	$46.2646	$46.26	$46.25	$46.30
Purchase #3	$109.79	12.785%	$123.8267	$123.83	$123.85	$123.80
Purchase #4	$51.35	5.836%	$54.3468	$54.35	$54.35	$54.30
Purchase #5	$233.29	11.150%	$259.3018	$259.30	$259.30	$259.30
Purchase #6	$150.52	11.323%	$167.5634	$167.56	$167.55	$167.60
Purchase #7	$242.57	7.816%	$261.5293	$261.53	$261.55	$261.50
7 purchase totals =	$855.04		$938.5349	$938.53	$938.55	$938.50