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	$44.90	12.458%	$50.4936	$50.49	$50.50	$50.50
Purchase #2	$180.32	6.720%	$192.4375	$192.44	$192.45	$192.40
Purchase #3	$12.88	7.586%	$13.8571	$13.86	$13.85	$13.90
Purchase #4	$94.31	9.611%	$103.3741	$103.37	$103.35	$103.40
Purchase #5	$137.47	4.674%	$143.8953	$143.90	$143.90	$143.90
Purchase #6	$147.73	5.483%	$155.83	$155.83	$155.85	$155.80
Purchase #7	$174.35	4.412%	$182.0423	$182.04	$182.05	$182.00
7 purchase totals =	$791.96		$841.9299	$841.93	$841.95	$841.90