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	$148.27	7.153%	$158.8758	$158.88	$158.90	$158.90
Purchase #2	$32.94	4.619%	$34.4615	$34.46	$34.45	$34.50
Purchase #3	$58.79	10.445%	$64.9306	$64.93	$64.95	$64.90
Purchase #4	$169.67	11.412%	$189.0327	$189.03	$189.05	$189.00
Purchase #5	$214.37	12.223%	$240.5724	$240.57	$240.55	$240.60
Purchase #6	$230.54	12.564%	$259.505	$259.51	$259.50	$259.50
Purchase #7	$55.94	3.132%	$57.692	$57.69	$57.70	$57.70
7 purchase totals =	$910.52		$1,005.0700	$1,005.07	$1,005.10	$1,005.10