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	$26.40	13.220%	$29.8901	$29.89	$29.90	$29.90
Purchase #2	$191.45	13.435%	$217.1713	$217.17	$217.15	$217.20
Purchase #3	$70.67	13.870%	$80.4719	$80.47	$80.45	$80.50
Purchase #4	$205.80	7.398%	$221.0251	$221.03	$221.05	$221.00
Purchase #5	$34.88	11.184%	$38.781	$38.78	$38.80	$38.80
Purchase #6	$179.33	3.415%	$185.4541	$185.45	$185.45	$185.50
Purchase #7	$48.44	5.123%	$50.9216	$50.92	$50.90	$50.90
7 purchase totals =	$756.97		$823.7151	$823.71	$823.70	$823.80