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	$33.33	6.187%	$35.3921	$35.39	$35.40	$35.40
Purchase #2	$39.92	6.359%	$42.4585	$42.46	$42.45	$42.50
Purchase #3	$30.37	12.546%	$34.1802	$34.18	$34.20	$34.20
Purchase #4	$92.79	5.258%	$97.6689	$97.67	$97.65	$97.70
Purchase #5	$185.86	6.711%	$198.3331	$198.33	$198.35	$198.30
Purchase #6	$214.27	6.241%	$227.6426	$227.64	$227.65	$227.60
Purchase #7	$248.62	12.578%	$279.8914	$279.89	$279.90	$279.90
7 purchase totals =	$845.16		$915.5668	$915.56	$915.60	$915.60