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	$39.44	5.280%	$41.5224	$41.52	$41.50	$41.50
Purchase #2	$133.89	7.422%	$143.8273	$143.83	$143.85	$143.80
Purchase #3	$64.39	13.365%	$72.9957	$73.00	$73.00	$73.00
Purchase #4	$11.59	9.597%	$12.7023	$12.70	$12.70	$12.70
Purchase #5	$136.65	6.384%	$145.3737	$145.37	$145.35	$145.40
Purchase #6	$77.94	3.299%	$80.5112	$80.51	$80.50	$80.50
Purchase #7	$21.69	7.740%	$23.3688	$23.37	$23.35	$23.40
7 purchase totals =	$485.59		$520.3014	$520.30	$520.25	$520.30