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	$135.69	12.706%	$152.9308	$152.93	$152.95	$152.90
Purchase #2	$77.81	6.593%	$82.94	$82.94	$82.95	$82.90
Purchase #3	$231.91	4.150%	$241.5343	$241.53	$241.55	$241.50
Purchase #4	$71.88	9.373%	$78.6173	$78.62	$78.60	$78.60
Purchase #5	$148.90	5.738%	$157.4439	$157.44	$157.45	$157.40
Purchase #6	$62.70	8.119%	$67.7906	$67.79	$67.80	$67.80
Purchase #7	$103.41	7.791%	$111.4667	$111.47	$111.45	$111.50
7 purchase totals =	$832.30		$892.7236	$892.72	$892.75	$892.60