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	$10.49	11.121%	$11.6566	$11.66	$11.65	$11.70
Purchase #2	$165.51	5.676%	$174.9043	$174.90	$174.90	$174.90
Purchase #3	$52.73	13.465%	$59.8301	$59.83	$59.85	$59.80
Purchase #4	$32.98	11.421%	$36.7466	$36.75	$36.75	$36.70
Purchase #5	$98.39	12.599%	$110.7862	$110.79	$110.80	$110.80
Purchase #6	$102.60	11.365%	$114.2605	$114.26	$114.25	$114.30
Purchase #7	$64.46	12.298%	$72.3873	$72.39	$72.40	$72.40
7 purchase totals =	$527.16		$580.5716	$580.58	$580.60	$580.60