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	$85.49	4.780%	$89.5764	$89.58	$89.60	$89.60
Purchase #2	$119.76	9.451%	$131.0785	$131.08	$131.10	$131.10
Purchase #3	$221.89	7.826%	$239.2551	$239.26	$239.25	$239.30
Purchase #4	$65.73	5.428%	$69.2978	$69.30	$69.30	$69.30
Purchase #5	$90.72	10.352%	$100.1113	$100.11	$100.10	$100.10
Purchase #6	$171.83	12.788%	$193.8036	$193.80	$193.80	$193.80
Purchase #7	$75.48	3.172%	$77.8742	$77.87	$77.85	$77.90
7 purchase totals =	$830.90		$900.9969	$901.00	$901.00	$901.10