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	$50.56	3.861%	$52.5121	$52.51	$52.50	$52.50
Purchase #2	$118.61	9.626%	$130.0274	$130.03	$130.05	$130.00
Purchase #3	$185.32	10.800%	$205.3346	$205.33	$205.35	$205.30
Purchase #4	$145.30	7.794%	$156.6247	$156.62	$156.60	$156.60
Purchase #5	$241.91	10.717%	$267.8355	$267.84	$267.85	$267.80
Purchase #6	$137.27	5.874%	$145.3332	$145.33	$145.35	$145.30
Purchase #7	$225.86	6.638%	$240.8526	$240.85	$240.85	$240.90
7 purchase totals =	$1,104.83		$1,198.5201	$1,198.51	$1,198.55	$1,198.40