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	$150.86	12.159%	$169.2031	$169.20	$169.20	$169.20
Purchase #2	$40.83	7.598%	$43.9323	$43.93	$43.95	$43.90
Purchase #3	$226.28	8.661%	$245.8781	$245.88	$245.90	$245.90
Purchase #4	$80.72	12.436%	$90.7583	$90.76	$90.75	$90.80
Purchase #5	$228.59	11.744%	$255.4356	$255.44	$255.45	$255.40
Purchase #6	$12.60	11.590%	$14.0603	$14.06	$14.05	$14.10
Purchase #7	$52.82	10.592%	$58.4147	$58.41	$58.40	$58.40
7 purchase totals =	$792.70		$877.6824	$877.68	$877.70	$877.70