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	$228.52	6.604%	$243.6115	$243.61	$243.60	$243.60
Purchase #2	$90.38	11.529%	$100.7999	$100.80	$100.80	$100.80
Purchase #3	$80.34	11.638%	$89.69	$89.69	$89.70	$89.70
Purchase #4	$21.62	3.679%	$22.4154	$22.42	$22.40	$22.40
Purchase #5	$184.78	11.275%	$205.6139	$205.61	$205.60	$205.60
Purchase #6	$160.69	10.688%	$177.8645	$177.86	$177.85	$177.90
Purchase #7	$155.83	12.530%	$175.3555	$175.36	$175.35	$175.40
7 purchase totals =	$922.16		$1,015.3507	$1,015.35	$1,015.30	$1,015.40