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	$20.55	4.581%	$21.4914	$21.49	$21.50	$21.50
Purchase #2	$134.88	8.623%	$146.5107	$146.51	$146.50	$146.50
Purchase #3	$197.36	9.365%	$215.8428	$215.84	$215.85	$215.80
Purchase #4	$57.30	13.347%	$64.9478	$64.95	$64.95	$64.90
Purchase #5	$110.65	11.338%	$123.1955	$123.20	$123.20	$123.20
Purchase #6	$114.42	5.410%	$120.6101	$120.61	$120.60	$120.60
Purchase #7	$97.57	6.478%	$103.8906	$103.89	$103.90	$103.90
7 purchase totals =	$732.73		$796.4889	$796.49	$796.50	$796.40