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	$142.76	3.201%	$147.3297	$147.33	$147.35	$147.30
Purchase #2	$176.98	13.276%	$200.4759	$200.48	$200.50	$200.50
Purchase #3	$201.61	12.332%	$226.4725	$226.47	$226.45	$226.50
Purchase #4	$130.28	13.728%	$148.1648	$148.16	$148.15	$148.20
Purchase #5	$97.28	6.252%	$103.3619	$103.36	$103.35	$103.40
Purchase #6	$60.93	9.789%	$66.8944	$66.89	$66.90	$66.90
Purchase #7	$40.38	13.291%	$45.7469	$45.75	$45.75	$45.70
7 purchase totals =	$850.22		$938.4461	$938.44	$938.45	$938.50