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	$237.28	13.149%	$268.4799	$268.48	$268.50	$268.50
Purchase #2	$31.39	10.616%	$34.7224	$34.72	$34.70	$34.70
Purchase #3	$27.98	5.742%	$29.5866	$29.59	$29.60	$29.60
Purchase #4	$230.78	13.867%	$262.7823	$262.78	$262.80	$262.80
Purchase #5	$172.30	9.453%	$188.5875	$188.59	$188.60	$188.60
Purchase #6	$64.78	13.537%	$73.5493	$73.55	$73.55	$73.50
Purchase #7	$78.36	3.222%	$80.8848	$80.88	$80.90	$80.90
7 purchase totals =	$842.87		$938.5928	$938.59	$938.65	$938.60