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	$176.82	5.452%	$186.4602	$186.46	$186.45	$186.50
Purchase #2	$95.56	13.499%	$108.4596	$108.46	$108.45	$108.50
Purchase #3	$94.99	5.785%	$100.4852	$100.49	$100.50	$100.50
Purchase #4	$125.74	11.594%	$140.3183	$140.32	$140.30	$140.30
Purchase #5	$47.55	3.302%	$49.1201	$49.12	$49.10	$49.10
Purchase #6	$106.58	5.564%	$112.5101	$112.51	$112.50	$112.50
Purchase #7	$35.40	13.513%	$40.1836	$40.18	$40.20	$40.20
7 purchase totals =	$682.64		$737.5371	$737.54	$737.50	$737.60