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	$201.51	10.382%	$222.4308	$222.43	$222.45	$222.40
Purchase #2	$88.78	7.348%	$95.3036	$95.30	$95.30	$95.30
Purchase #3	$143.29	8.711%	$155.772	$155.77	$155.75	$155.80
Purchase #4	$26.50	7.415%	$28.465	$28.47	$28.45	$28.50
Purchase #5	$131.90	4.728%	$138.1362	$138.14	$138.15	$138.10
Purchase #6	$26.92	7.618%	$28.9708	$28.97	$28.95	$29.00
Purchase #7	$237.95	11.108%	$264.3815	$264.38	$264.40	$264.40
7 purchase totals =	$856.85		$933.4599	$933.46	$933.45	$933.50