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	$49.85	4.541%	$52.1137	$52.11	$52.10	$52.10
Purchase #2	$109.58	12.788%	$123.5931	$123.59	$123.60	$123.60
Purchase #3	$19.43	12.476%	$21.8541	$21.85	$21.85	$21.90
Purchase #4	$181.54	5.284%	$191.1326	$191.13	$191.15	$191.10
Purchase #5	$59.40	9.195%	$64.8618	$64.86	$64.85	$64.90
Purchase #6	$245.87	7.486%	$264.2758	$264.28	$264.30	$264.30
Purchase #7	$112.30	9.128%	$122.5507	$122.55	$122.55	$122.60
7 purchase totals =	$777.97		$840.3818	$840.37	$840.40	$840.50