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	$40.56	11.616%	$45.2714	$45.27	$45.25	$45.30
Purchase #2	$62.90	9.282%	$68.7384	$68.74	$68.75	$68.70
Purchase #3	$238.45	9.428%	$260.9311	$260.93	$260.95	$260.90
Purchase #4	$150.32	12.720%	$169.4407	$169.44	$169.45	$169.40
Purchase #5	$136.50	11.720%	$152.4978	$152.50	$152.50	$152.50
Purchase #6	$13.60	5.627%	$14.3653	$14.37	$14.35	$14.40
Purchase #7	$83.80	8.342%	$90.7906	$90.79	$90.80	$90.80
7 purchase totals =	$726.13		$802.0353	$802.04	$802.05	$802.00