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	$78.36	5.254%	$82.477	$82.48	$82.50	$82.50
Purchase #2	$101.69	8.857%	$110.6967	$110.70	$110.70	$110.70
Purchase #3	$238.95	5.253%	$251.502	$251.50	$251.50	$251.50
Purchase #4	$154.79	6.160%	$164.3251	$164.33	$164.35	$164.30
Purchase #5	$81.81	6.716%	$87.3044	$87.30	$87.30	$87.30
Purchase #6	$35.95	10.797%	$39.8315	$39.83	$39.85	$39.80
Purchase #7	$92.29	12.160%	$103.5125	$103.51	$103.50	$103.50
7 purchase totals =	$783.84		$839.6492	$839.65	$839.70	$839.60