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	$32.60	10.364%	$35.9787	$35.98	$36.00	$36.00
Purchase #2	$53.43	9.391%	$58.4476	$58.45	$58.45	$58.40
Purchase #3	$143.34	11.683%	$160.0864	$160.09	$160.10	$160.10
Purchase #4	$113.62	12.412%	$127.7225	$127.72	$127.70	$127.70
Purchase #5	$123.43	12.332%	$138.6514	$138.65	$138.65	$138.70
Purchase #6	$119.86	9.689%	$131.4732	$131.47	$131.45	$131.50
Purchase #7	$238.32	5.234%	$250.7937	$250.79	$250.80	$250.80
7 purchase totals =	$824.60		$903.1535	$903.15	$903.15	$903.20