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	$158.97	10.853%	$176.223	$176.22	$176.20	$176.20
Purchase #2	$208.33	5.418%	$219.6173	$219.62	$219.60	$219.60
Purchase #3	$56.64	4.715%	$59.3106	$59.31	$59.30	$59.30
Purchase #4	$184.46	3.138%	$190.2484	$190.25	$190.25	$190.20
Purchase #5	$65.61	7.490%	$70.5242	$70.52	$70.50	$70.50
Purchase #6	$131.97	7.707%	$142.1409	$142.14	$142.15	$142.10
Purchase #7	$78.67	7.747%	$84.7646	$84.76	$84.75	$84.80
7 purchase totals =	$884.65		$942.8290	$942.82	$942.75	$942.70