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	$110.83	11.856%	$123.97	$123.97	$123.95	$124.00
Purchase #2	$222.72	12.514%	$250.5912	$250.59	$250.60	$250.60
Purchase #3	$11.79	4.609%	$12.3334	$12.33	$12.35	$12.30
Purchase #4	$88.54	7.109%	$94.8343	$94.83	$94.85	$94.80
Purchase #5	$147.65	11.636%	$164.8306	$164.83	$164.85	$164.80
Purchase #6	$205.56	9.476%	$225.0389	$225.04	$225.05	$225.00
Purchase #7	$35.75	8.861%	$38.9178	$38.92	$38.90	$38.90
7 purchase totals =	$822.84		$910.5162	$910.51	$910.55	$910.40