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	$115.72	4.304%	$120.7006	$120.70	$120.70	$120.70
Purchase #2	$70.77	11.466%	$78.8845	$78.88	$78.90	$78.90
Purchase #3	$90.54	10.562%	$100.1028	$100.10	$100.10	$100.10
Purchase #4	$146.88	13.702%	$167.0055	$167.01	$167.00	$167.00
Purchase #5	$175.98	3.654%	$182.4103	$182.41	$182.40	$182.40
Purchase #6	$23.88	13.367%	$27.072	$27.07	$27.05	$27.10
Purchase #7	$116.73	9.665%	$128.012	$128.01	$128.00	$128.00
7 purchase totals =	$740.50		$804.1877	$804.18	$804.15	$804.20