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	$223.98	8.265%	$242.4919	$242.49	$242.50	$242.50
Purchase #2	$20.70	8.597%	$22.4796	$22.48	$22.50	$22.50
Purchase #3	$164.28	13.179%	$185.9305	$185.93	$185.95	$185.90
Purchase #4	$82.90	4.448%	$86.5874	$86.59	$86.60	$86.60
Purchase #5	$173.76	5.364%	$183.0805	$183.08	$183.10	$183.10
Purchase #6	$94.31	8.640%	$102.4584	$102.46	$102.45	$102.50
Purchase #7	$50.91	6.281%	$54.1077	$54.11	$54.10	$54.10
7 purchase totals =	$810.84		$877.1360	$877.14	$877.20	$877.20