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	$30.33	3.164%	$31.2896	$31.29	$31.30	$31.30
Purchase #2	$185.49	12.663%	$208.9786	$208.98	$209.00	$209.00
Purchase #3	$120.63	4.742%	$126.3503	$126.35	$126.35	$126.40
Purchase #4	$80.45	5.627%	$84.9769	$84.98	$85.00	$85.00
Purchase #5	$10.77	3.410%	$11.1373	$11.14	$11.15	$11.10
Purchase #6	$22.76	12.121%	$25.5187	$25.52	$25.50	$25.50
Purchase #7	$92.29	11.857%	$103.2328	$103.23	$103.25	$103.20
7 purchase totals =	$542.72		$591.4842	$591.49	$591.55	$591.50