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	$115.98	4.216%	$120.8697	$120.87	$120.85	$120.90
Purchase #2	$92.52	11.524%	$103.182	$103.18	$103.20	$103.20
Purchase #3	$182.77	12.123%	$204.9272	$204.93	$204.95	$204.90
Purchase #4	$98.60	5.223%	$103.7499	$103.75	$103.75	$103.70
Purchase #5	$37.97	6.628%	$40.4867	$40.49	$40.50	$40.50
Purchase #6	$236.86	11.605%	$264.3476	$264.35	$264.35	$264.30
Purchase #7	$127.52	10.669%	$141.1251	$141.13	$141.15	$141.10
7 purchase totals =	$892.22		$978.6882	$978.70	$978.75	$978.60