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	$160.97	6.560%	$171.5296	$171.53	$171.55	$171.50
Purchase #2	$69.64	10.772%	$77.1416	$77.14	$77.15	$77.10
Purchase #3	$185.57	8.240%	$200.861	$200.86	$200.85	$200.90
Purchase #4	$162.68	4.409%	$169.8526	$169.85	$169.85	$169.90
Purchase #5	$76.97	13.730%	$87.538	$87.54	$87.55	$87.50
Purchase #6	$46.42	9.230%	$50.7046	$50.70	$50.70	$50.70
Purchase #7	$136.67	4.252%	$142.4812	$142.48	$142.50	$142.50
7 purchase totals =	$838.92		$900.1086	$900.10	$900.15	$900.10