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	$35.51	12.111%	$39.8106	$39.81	$39.80	$39.80
Purchase #2	$211.71	5.652%	$223.6758	$223.68	$223.70	$223.70
Purchase #3	$130.92	4.385%	$136.6608	$136.66	$136.65	$136.70
Purchase #4	$96.54	3.143%	$99.5743	$99.57	$99.55	$99.60
Purchase #5	$200.42	12.220%	$224.9113	$224.91	$224.90	$224.90
Purchase #6	$178.53	4.613%	$186.7656	$186.77	$186.75	$186.80
Purchase #7	$82.26	10.239%	$90.6826	$90.68	$90.70	$90.70
7 purchase totals =	$935.89		$1,002.0810	$1,002.08	$1,002.05	$1,002.20